RU2534222C1 - Nearly invisible moving objects detection method - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method is implemented owing to applying operations providing maximisation of output signal-to-noise ratio and based on detection of maximum proper values of correlation arrays used at formation and compensation of an illumination transmitter being coherent interference of a forward signal, as well as at separation and optimum coherent detection of useful signals received after compensation of interference and adjusted as per the specified variety of hypothetic values of spatial coordinates, directions and speeds of object movement.

EFFECT: increasing detection range of nearly invisible moving objects.

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Description

The invention relates to radio engineering and can be used in monitoring systems of land, sea and air space using direct and scattered objects of radio signals emitted by many uncontrolled and monitored transmitters of electronic systems for various purposes.

Achieving high efficiency in the detection, localization and identification of land, sea and air objects is limited by significant a priori uncertainty in the size, reflecting properties and states (spatial coordinates, direction and speed of movement) of the object, as well as the imperfection of the known methods for detecting and tracking moving objects.

The technology of covert detection and tracking of moving objects using natural radio illumination of targets created at a variety of frequencies by radio emissions from transmitters for various purposes in the short, meter, decimeter and centimeter wavelengths: broadcast (VHF FM broadcasting, DVB-T2 digital television), information (communication ) and measuring (control, navigation), has not yet received sufficient distribution, despite the fact that it can significantly increase stealth and search efficiency and space nstvennoy localization of a broad class of mobile objects.

A known method for detecting subtle moving objects [1], which consists in selecting a transmitter emitting a spread spectrum radio signal, synchronously receiving an array of multipath radio signals including a direct transmitter radio signal and scattered radio signals from this transmitter from the objects, synchronously converting the ensemble of radio signals received by the antennas into digital signals, direct and compressed scattered signals are formed from digital signals, the selected direct and scattered signals are compared and time Variable delays, Doppler shifts, and directions of arrival of scattered signals, in terms of time delays, Doppler shifts, and directions of arrival, perform detection and spatial localization of moving objects.

This method does not contain operations to suppress coherent interference in the form of a direct radio signal from the transmitter and, as a result, provides effective detection of only very large closely spaced moving objects.

More effective is the method for detecting subtle moving objects [2], free from this drawback and selected as a prototype.

According to this method, direct and scattered by mobile objects broadband radio signals emitted by transmitters of various electronic systems are coherently received by the antenna array multi-beam radio signals including direct and scattered radio signals, synchronously transform the ensemble of radio signals received by the antennas into digital signals, digital signals are combined into a matrix digital signal and remember, from the matrix digital signal form the signal of the spatial correlation matrix, to which, together with the guidance vector signal, determined by the azimuthal elevation direction of direct radio signal reception, wavelength, and lattice geometry, is converted into an optimal weight vector signal, the matrix digital signal is converted into a direct digital signal, which is stored in a complex and mutually dependent time shift correlation functions (VKF) between the digital signal of an individual antenna and a direct digital signal, determine the maximum value of the module of each complex VKF and phi they compute the values of the complex VKF corresponding to these maxima, calculate the difference digital signals, form complex two-dimensional cross-correlation functions (DKKF) depending on the time and frequency shifts between each difference digital signal and the direct digital signal, average the modules of the complex DKFV, average the number from the maxima of the averaged DKFV compressed signals and fix the values of time delay and absolute Doppler shift of each p-th compressed signal, identify the corresponding individual at the maximum of the averaged DKFV, the components of the complex DKFV as the pth signal compressed in time and frequency, isolate and store the values of the components of the complex DKFV, the time delay and the absolute Doppler shift of each rth compressed signal, according to the extracted values of the rth identified components of the complex DKFV synthesize a complex two-dimensional angular spectrum, the maximum modulus of which determines the azimuthal elevation direction of arrival of the p-th compressed signal from the values of delay and absolute Doppler with Whig approach elevation and azimuthal direction of arrival detect and determine the spatial coordinates of the movable object.

The prototype method due to the presence of adaptive spatial filtering operations and operations of electronic compensation of coherent interference in the form of a powerful direct radio signal of the backlight transmitter provides detection of a wider class of moving objects. However, the prototype method contains the operation of forming a classic two-dimensional cross-correlation function, which contains high side lobes masking the signals of distant and weakly scattering objects.

Thus, the disadvantage of the prototype method is the limited detection range of subtle moving objects.

The technical result of the invention is to increase the detection range of subtle moving objects.

An increase in the detection range of subtle moving objects is achieved through the use of new operations that maximize the output signal-to-noise ratio and are based on finding the largest eigenvalues of the correlation matrices used in the formation and compensation of the direct signal of the backlight transmitter, which is coherent interference, as well as in the selection and optimal coherent detection of useful signals received after interference compensation and corrected for a given set of hypotheses physical states (spatial coordinates, direction and speed of movement) of objects.

- номер антенны, объединяют откорректированные цифровые сигналы s_n в матрицу откорректированных сигналов Ф, которую преобразуют в пространственную корреляционную матрицу откорректированных сигналов G=Ф^НФ и в сигнальную матрицу F=ФФ^Н, находят наибольшее собственное значение корреляционной матрицы откорректированных сигналов G и соответствующий найденному собственному значению главный собственный вектор сигнальной матрицы F, идентифицируют найденное значение главного собственного вектора как прямой цифровой сигнал u, который запоминают, формируют нормированный коэффициент взаимной корреляции β_n=u^Н s _n/║u║² между прямым цифровым сигналом u и откорректированным цифровым сигналом s_n каждой антенны, получают разностный цифровой сигнал каждой антенны

, преобразуют разностный цифровой сигнал каждой антенны

в откорректированный по временной задержке и доплеровскому сдвигу частоты на заданном множестве гипотетических состояний объектов разностный цифровой сигнал

, откорректированные разностные цифровые сигналы

всех антенн объединяют в матрицу разностных сигналов

, матрицу разностных сигналов

преобразуют в пространственную корреляционную матрицу разностных сигналов

, находят наибольшее собственное значение корреляционной матрицы разностных сигналов

, после сравнения которого с порогом принимают решение об обнаружении подвижного объекта с текущим гипотетическим состоянием объекта.The technical result is achieved by the fact that in the method for detecting subtle moving objects, which consists in the use of direct and scattered by moving objects broadband radio signals emitted by transmitters of electronic systems for various purposes, coherent array antenna reception of multi-beam radio signals, including direct and scattered radio signals, synchronously converts received antennas, radio signals into digital signals, according to the invention, convert the digital signal of each antenna into ktirovanny of time delay and Doppler frequency shift for the known state of the transmitter digital signal s_nwhere

 - antenna number, combine the corrected digital signals s_n into the matrix of corrected signals Ф, which is converted into the spatial correlation matrix of corrected signals G = Ф^NФ and to the signal matrix F = ФФ^Nfind the largest eigenvalue of the correlation matrix of the corrected signals G and the main eigenvector of the signal matrix F corresponding to the found eigenvalue, identify the found value of the main eigenvector as a direct digital signal u, which is stored, form a normalized cross-correlation coefficient β_n= u^N s _n/ ║u║² between the direct digital signal u and the corrected digital signal s_n each antenna, receive a differential digital signal of each antenna

convert the differential digital signal of each antenna

 in the time difference and Doppler frequency shift corrected for a given set of hypothetical states of objects, a difference digital signal

, corrected differential digital signals

 all antennas are combined into a matrix of difference signals

matrix of difference signals

 transform into a spatial correlation matrix of difference signals

find the largest eigenvalue of the correlation matrix of difference signals

, after comparing it with a threshold, they decide to detect a moving object with the current hypothetical state of the object.

The operation of the method is illustrated in the drawing.

A device in which the proposed method is implemented includes a series-connected antenna system 1, an N-channel frequency converter (RF) 2, an N-channel quadrature sampling device 3, a computer 4, and a display device 5.

In turn, the calculator 4 includes a shift device 4-1, a differential signal driver 4-2, a shift device 4-3, a detection device 4-4.

The shear device 4-1 and the frequency converter 2 are connected to external systems to obtain information about the radiation parameters of the selected backlight transmitter. In addition, the shift device 4-1 receives information from external systems about the state vector of the backlight transmitter in the form of: spatial coordinates, direction and speed of movement when choosing a mobile transmitter or only spatial coordinates when choosing a stationary transmitter. Communication with external systems for the purpose of simplification is not shown.

Antenna system 1 contains N antennas with numbers n = 1 ... N, combined in an array. The antenna array can be of any spatial configuration: flat rectangular, flat annular or three-dimensional, in particular conformal.

The bandwidth of each channel of the multi-channel RFI 2 provides reception of a broadband signal. In addition, multi-channel RFR 2 and device 3 are made with a common local oscillator, which provides coherent reception of radio signals. For periodic calibration of channels using an external signal source in order to eliminate their amplitude-phase non-identity, the RFI 2 provides the connection of one of the antennas instead of all the antennas of the array. Calibration by internal signal source is possible. In this case, a noise generator can be used, the output of which can also be connected instead of all antennas for periodic calibration of channels. If the resolution and speed of the ADCs that are part of device 3 are sufficient for direct analog-to-digital conversion of the input signals, then instead of the RFI 2, a frequency-selective band-pass filter and amplifier can be used. In other words, the analog part of the device that implements the proposed method can be built on the principle of direct amplification.

A device that implements the proposed method works as follows.

After receiving information about the radiation parameters of the selected backlight transmitter, the RFI 2 tunes to the frequency of the backlight radio signal.

Multipath radio signals, including a spread spectrum direct signal emitted by the illumination transmitter and radio signals of this transmitter scattered by objects, are coherently received by spatially separated receiving antennas of the array 1.

The time-dependent total radio signal x _n (t) received by each antenna array 1 in RFI 2 is coherently transferred to a lower frequency.

The ensemble of received radio signals x _n (t) formed in RFH 2 is synchronously converted in device 3 into an ensemble of complex digital signals x _n (z), where z = 1, ..., Z is the number of the time reference of the signal. Digital signals x _n = [x _n (1), ..., x _n (z), ..., x _n (Z)] are sent to device 4-1, where they are synchronously recorded at a given time interval.

In addition, in the device 4-1, the following actions are performed:

converted digital signal x _n in each antenna corrected by the time delay and Doppler frequency shift for the known state of the transmitter digital signal s _n.

In this case, information on the state of the transmitter in the form of current spatial coordinates, the direction and speed of its movement, if a mobile transmitter is selected, and in the form of only spatial coordinates, if a stationary transmitter is selected, is received from external systems. The conversion is carried out in a known manner [3].

, где µ_n - значение комплексного коэффициента рассеяния цели, u(z) - копия сигнала передатчика, принятого каждой n-ой антенной сигнала, корректируется по следующей формуле

. Отметим, если передатчик является стационарным, то значение доплеровского сдвига частоты ℓ_n его сигнала равно нулю и принятый каждой n-ой антенной сигнал корректируется только по задержке;So, the expected value of the time delay τ _n is calculated from the spatial coordinates of the transmitter, and the expected value of the Doppler frequency shift ℓ _{n of the} signal received by each nth antenna is calculated from the direction and speed of the transmitter. After that, each countdown

, where μ _n is the value of the complex scattering coefficient of the target, u (z) is a copy of the transmitter signal received by each n-th antenna signal, is adjusted according to the following formula

. Note that if the transmitter is stationary, then the value of the Doppler frequency shift ℓ _{n of} its signal is zero and the signal received by each nth antenna is corrected only for the delay;

the corrected digital signals s _n are combined into the matrix of corrected signals Ф = (s ₁ , ..., s _N ) of size Z × N;

the matrix of corrected signals Ф is transformed into the N × N spatial correlation matrix of corrected signals G = Ф ^Н Ф and into Z × Z the signal matrix F = ФФ ^Н ;

the largest eigenvalue of the correlation matrix of the corrected signals G is found and the main eigenvector of the signal matrix F corresponding to the found eigenvalue

The greatest eigenvalue and the main eigenvector are found by known methods [4, 5]. This operation makes a significant contribution to increasing the sensitivity and, therefore, the detection range of subtle objects, as it maximizes the output signal-to-noise ratio during subsequent compensation of coherent noise in the form of a direct signal from the backlight transmitter;

the found value of the main eigenvector is identified as a direct digital signal u.

The direct digital signal u enters the shaper 4-2, where it is stored.

In the shaper 4-2, the following actions are performed:

a normalized cross-correlation coefficient β is formed_n= u^N s _n/ ║u║² between the direct digital signal u and the corrected digital signal s_n each antenna;

.the difference digital signal of each antenna is obtained

.

антенн поступают в устройство 4-3.Differential digital signals

antennas enter the device 4-3.

The device 4-3 performs the following actions:

в откорректированный по временной задержке и доплеровскому сдвигу частоты на заданном множестве гипотетических состояний объектов разностный цифровой сигнал

. Преобразование разностного цифрового сигнала каждой антенны

в откорректированный разностный цифровой сигнал

также осуществляется известным способом [3]. При этом гипотетическое состояние объекта описывается несколькими гипотетическими (ожидаемыми) величинами: пространственными координатами, направлением и скоростью движения подвижного объекта;the differential digital signal of each antenna is converted

in the time difference and Doppler frequency shift corrected for a given set of hypothetical states of objects, a difference digital signal

. Converting a difference digital signal of each antenna

into the corrected difference digital signal

also carried out in a known manner [3]. In this case, the hypothetical state of the object is described by several hypothetical (expected) values: spatial coordinates, direction and speed of the moving object;

всех антенн объединяются в Z×N матрицу разностных сигналов

;corrected differential digital signals

all antennas are combined into a Z × N matrix of difference signals

;

преобразуется в N×N пространственную корреляционную матрицу разностных сигналов

.differential signal matrix

the spatial correlation matrix of difference signals is converted to N × N

.

поступает в устройство 4-4.Spatial correlation matrix of difference signals

enters the device 4-4.

.The device 4-4 is the largest eigenvalue of the correlation matrix of difference signals

.

This operation also makes a significant contribution to increasing the sensitivity and, therefore, the detection range of subtle objects, as it maximizes the output signal-to-noise ratio when extracting useful signals received after interference compensation and corrected for a given set of hypothetical states of objects;

с порогом в устройстве 4-4 принимается решение об обнаружении подвижного объекта с текущим гипотетическим состоянием объекта. Гипотетическое состояние объекта описывается гипотетическими пространственными координатами, гипотетическим направлением и гипотетической скоростью движения объекта. Порог выбирается, исходя из минимизации вероятности ложной тревоги.After comparing the eigenvalue of the correlation matrix of the difference signals $$\tilde{G}$$

with a threshold in the device 4-4, a decision is made to detect a moving object with the current hypothetical state of the object. The hypothetical state of the object is described by hypothetical spatial coordinates, the hypothetical direction and the hypothetical speed of the object. The threshold is selected based on minimizing the likelihood of a false alarm.

The device 5 displays the results of the detection and spatial localization of objects.

Thus, through the use of new operations that maximize the output signal-to-noise ratio and are based on finding the largest eigenvalues of the correlation matrices used in the formation and compensation of the direct signal of the backlight transmitter, which is coherent interference, as well as in the selection and optimal coherent detection of useful signals, obtained after the compensation of interference and corrected on a variety of hypothetical states of objects, it is possible to solve the problem with achieving the specified technical result.

Information sources

1. US patent 6703968 B2, cl. G01S 13/87, 2004

2. RU, patent, 2444754, cl. G01S 13/02, 2012

3. Reference radar. Ed. M. Skolnik. New York, 1970. Transl. from English (in four volumes) under the general ed. K.N. Trofimova. Volume 1. Basics of radar. Ed. Ya.S. Yitzhoki. M., "Owls. Radio ”, 1976, 456 p.

4. Wilkison J. X. Algebraic eigenvalue problem. - M.: Nauka, 1970.564 s.

5. Marple S.L. (ml.). Digital spectral analysis and its applications. M .: "World", 1990.584 s.

Claims (1)

A method for detecting inconspicuous moving objects, which consists in the fact that they use direct and scattered by moving objects broadband radio signals emitted by transmitters of various electronic systems, coherently receive a multipath radio signal array including direct and scattered radio signals, synchronously converts the received radio signals into antennas into digital signals by converting the digital signal of each antenna into time delay corrected and Doppler to a frequency shift for a known transmitter state is a digital signal s _n , where

- antenna number, combine the corrected digital signals s _n into the matrix of corrected signals Ф, which is converted into the spatial correlation matrix of corrected signals G = Ф ^Н Ф and into the signal matrix F = ФФ ^Н , find the largest eigenvalue of the correlation matrix of corrected signals G and corresponding to the found the eigenvalue of the main eigenvector of the signal matrix F, identify the found value of the main eigenvector as a direct digital signal u, which nayut form a normalized cross-correlation coefficient β _n = u ⁿ s _n / ║u║ ² between the direct digital signal u and the corrected digital signal s _n each antenna differential digital receive signal of each antenna

convert the differential digital signal of each antenna

in the time difference and Doppler frequency shift corrected for a given set of hypothetical states of objects, a difference digital signal

, corrected differential digital signals

all antennas are combined into a matrix of difference signals

matrix of difference signals

transform into a spatial correlation matrix of difference signals

find the largest eigenvalue of the correlation matrix of difference signals $$\tilde{G}$$

, after comparing it with a threshold, they decide to detect a moving object with the current hypothetical state of the object.