RU2571950C1 - Method for radio monitoring of radio-silent objects - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method is carried out using additional information on the fine structure of echo signals of the Doppler signature of objects and using new operations, which enable to compare and merge scattered signals based on frequency (Doppler shift), time (delay) and angular (amplitude-phase distribution) information.

EFFECT: high probability of detection and enabling classification of radio-silent objects.

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Description

The invention relates to radio engineering and can be used in covert control systems of air, ground and surface space using uncontrolled and controlled transmitters of electronic systems for various purposes, emitting signals with a wide spectrum.

The achievement of high efficiency in the detection, localization and classification of objects operating in the radio silence mode is limited by significant a priori uncertainty in size, spatial orientation, their reflective properties, and the imperfection of known radio monitoring methods.

The technology of passive radio monitoring of radio-silent objects using natural target illumination created at a variety of frequencies by radio emissions from various transmitters in the short, meter, decimeter and centimeter wavelengths: broadcast (commercial broadcasting, terrestrial and satellite television), information (communication), and measurement (control, navigation), has not yet received sufficient distribution, despite the fact that it can significantly increase the stealth and effectiveness of radio trol broad class of objects.

It is known that due to the movement of the target, the echo signal from its body experiences a Doppler frequency shift. In addition, vibration or rotation of the target and individual parts of its structure cause additional modulation of the echo signal, which forms two side frequency bands near the main Doppler echo signal. This effect, known as micro-Doppler modulation or micro-Doppler signature (characteristic feature, complex target characteristic), provides additional unique information about the type of each target and can be used to detect and classify moving and even stationary targets, for example, a wide class of propeller (rotary-wing) manned and unmanned vehicles moving in air, on land and on water, as well as functioning stationary helicopters, quadrocopters, ekranoplanes and amphibious boats Bii.

A known method of radio monitoring of radio-silent objects [1], which consists in the fact that they select a radio transmitter emitting a continuous monochromatic or amplitude-modulated signal, coherently receive a multipath signal by the antenna array, including a direct transmitter signal and the signals of this transmitter scattered by objects, synchronously transform the ensemble of signals received by the antennas into digital signals, from digital signals form signals cleared from the direct signal of the transmitter, determined by the cleared signals and the number of received scattered signals, their amplitudes, Doppler frequency shifts and corresponding to each scattered signal components of the complex time spectrum of the signal received by each antenna are determined, which determine the azimuthal elevation directions of arrival of each scattered signal, perform detection and estimate the bistatic speed of radio-silent objects from Doppler values shift and azimuth-elevation direction of reception of scattered signals.

This method does not provide a determination of the range to detected objects.

More effective is the method of radio monitoring of radio-silent objects [2], free from this drawback and selected as a prototype. According to this method:

choose a radio transmitter emitting a spread spectrum signal,

synchronously receive the multipath signals by the antenna array, including the direct transmitter signal and the signals of this transmitter scattered by the objects,

synchronously transform the ensemble of signals received by the antennas into digital signals,

from digital signals form signals of complex frequency-time images of antennas,

which determine the number of scattered signals, their Doppler frequency shifts and time delays, as well as

the components of complex time-frequency images corresponding to the found shifts and delays are distinguished, of which

form a vector signal of the amplitude-phase distribution (AFR) of each scattered signal,

which, together with the values of the Doppler frequency shift and time delay, is used for the detection and spatial localization of a radio-silent object.

The prototype method provides spatial localization of targets, which increases the efficiency of covert tracking of radio-silent objects.

The disadvantage of this method is the low probability of detection and the inability to classify radio-silent objects.

This is due to the fact that the prototype method does not have operations for analyzing echo signals of the Doppler signature of controlled objects, which significantly reduces the probability of detection and does not allow the classification of a wide class of radio-silent objects.

The technical result of the invention is to increase the likelihood of detection and enable classification of radio-silent objects.

An increase in the probability of detection and the possibility of classifying radio-silent objects is achieved by:

- the use of additional information about the fine structure of the echo signals of the Doppler signature of the objects (the main Doppler echo from the body of the object and additional echo signals of the micro-Doppler signature of the object);

- the use of new operations for generating echo signals of the Doppler signature of objects that implement the comparison and combining of scattered signals based on the frequency (Doppler shift), time (delay) and angular (amplitude-phase distribution of the signals received by the antenna array) information.

The technical result is achieved by the fact that in the method of radio monitoring of radio-silent objects, which consists in choosing a radio transmitter emitting a signal with a spread spectrum, synchronously receiving an array of antennas with multipath signals, including a direct signal from the transmitter and the signals scattered by objects from this transmitter, synchronously transform the ensemble of signals received by the antennas into digital signals, from digital signals form signals of complex frequency-time images of antennas, which determine the number of scatter signals, their Doppler frequency shifts and time delays, and also select the components of complex time-frequency images corresponding to the found shifts and delays, from which the amplitude-phase distribution (AFR) vector signal of each scattered signal is formed, according to the invention, scattered signals and signals are compared with different Doppler frequency shifts but coinciding delays and AFR are combined into a multi-frequency signal with a symmetric spectrum, which is identified as an echo signal Doppler signature of the detected object, the echo signals of the Doppler signature determine the azimuth-elevation direction, spatial coordinates, bistatic speed and classify the detected objects.

The operation of the method is illustrated by drawings:

FIG. 1. The structural diagram of a device that implements the proposed method for radio monitoring of radio-silent objects;

FIG. 2. Echo signals of the Doppler signature: a) a moving object; b) a stationary object.

FIG. 3. Features of the functioning of the device that implements the proposed method.

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

In turn, the calculator 4 includes a device for generating time-frequency images 4-1, a detection and classification device 4-2.

Devices 4-1 and 4-2 can be made in single-channel or multi-channel versions. Consider a multi-channel option that provides the highest possible speed of detection and classification of radio-silent objects.

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 multichannel RFI 2 provides the simultaneous reception of the transmitter radio signal. In addition, the RFI 2 and the device 3 are made with a common reference generator, 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 bit depth 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.

A multipath radio signal, including the direct signal of a selected transmitter emitting a spread-spectrum signal, and the signals of this transmitter scattered by objects, are coherently received by the grating antennas 1. The time-dependent total radio signal x _n (t) received in each antenna grating t in RF2 is coherently transferred to lower frequency, where n = 1, ..., N is the antenna number.

, где z - номер временного отсчета сигнала.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 $$x_{nz}^{\text{'}\text{'}}$$

where z is the time reference number of the signal.

синхронно регистрируются на заданном временном интервале в устройстве формирования изображений 4-1. Кроме того, в устройстве 4-1 выполняются следующие действия:Digital signals $$x_{nz}^{\text{'}\text{'}}$$

synchronously recorded at a predetermined time interval in the image forming apparatus 4-1. In addition, in the device 4-1, the following actions are performed:

формируется сигнал комплексного частотно-временного изображения (ЧВИ) каждой антенны.1) from digital signals $$x_{nz}^{\text{'}\text{'}}$$

a signal of a complex time-frequency image (CVI) of each antenna is formed.

The formation of signals of complex FWM antennas is carried out by known methods.

So, following the method [2], the following actions are performed:

- from a digital signal, a direct transmitter signal and signals of each antenna cleared from a direct transmitter signal are formed;

- time-dependent and frequency-shift-dependent complex two-dimensional cross-correlation functions (DKKF) between the cleaned signal of each antenna and the direct signal of the transmitter are calculated. Formed from the cleaned signal of a separate antenna, the FWF is a complex FWI that describes the distribution of scattered signals over the Doppler frequency and time delay.

Another more advanced method of generating complex FWM signals does not require the operations of generating signals of each antenna purified from a direct transmitter signal [3]. According to this method, the following actions are performed:

- a direct transmitter signal is formed from digital signals;

- from the direct signal and the signal of an individual antenna, an integrated FWI signal is generated iteratively, which describes the distribution of scattered signals over the Doppler frequency and time delay;

2) from the signals of complex FWM antennas, the number L of scattered signals, their Doppler frequency shifts ω _ℓ and time delays τ _{pℓ are determined} , and the corresponding shifts and

каждого рассеянного сигнала, где p,ℓ - номер дискретного значения задержки и доплеровского сдвига частоты соответственно, а […]^T - означает операцию транспонирования.delays, the components of complex CVIs k _npℓ , from which the AFR vector signal is formed

each scattered signal, where p, ℓ is the number of the discrete value of the delay and Doppler frequency shift, respectively, and [...] ^T - means the transpose operation.

Received in the device 4-1, the number L of scattered signals, the values of the Doppler frequency shift ω _ℓ and the delay τ _pℓ , as well as the vector AFR signal K _{pℓ of} each scattered signal are sent to the device 4-2, where they are stored.

After that, the device 4-2 performs the following actions:

1) scattered signals and signals with different Doppler frequency shifts are compared, but coincident delays and AFR are combined into a multi-frequency signal with a symmetric spectrum.

Comparison and integration of scattered signals is carried out on the basis of frequency (Doppler shift), time (delay) and angular information in two stages.

In this case, the previously noted fact is used that the echo signals of an individual object due to vibration or rotation of individual parts of its structure acquire a symmetric structure of the frequency spectrum, characteristic of amplitude or frequency modulation of signals, consisting of the main echo signal from the object body and symmetrically located signals of the lower and upper sidebands resulting from modulation of the main echo. In addition, it is taken into account that the signals scattered by an individual object (the main echo signal from the object body and additional echo signals of the lower and upper side bands) come from one spatial point and, as a result, at the reception point they coincide in delay (range) and in AFR (direction of arrival).

At the first stage, the following actions are performed:

, k, ℓ, m=1, …, L, где δ, δ₁, δ₂ - порог по частоте, значение которого выбирается исходя из минимума вероятности пропуска сигнала, и совпадающими задержками τ_pk, τ_pℓ, τ_pm.- scattered signals are compared and scattered signals are selected with frequencies satisfying the following conditions: ω _k <ω _ℓ <ω _m ,

, k, ℓ, m = 1, ..., L, where δ, δ ₁ , δ ₂ is the frequency threshold, the value of which is selected based on the minimum probability of missing the signal, and the coincident delays τ _pk , τ _pℓ , τ _pm .

Physically, this operation can be considered as a combination of separate, coincident in delay (range), scattered signals into groups of multi-frequency signals with a symmetric spectrum. Each group is characterized by the presence of a main echo signal with a central frequency ω _ℓ , as well as two or more additional echo signals symmetrically located at frequencies ω _k and ω _m and coinciding in delay (range).

An example of echo signals in the coordinates "delay-Doppler frequency shift" and "amplitude-Doppler frequency shift" of a moving (approaching) a) and stationary b) object is shown in FIG. 2.

In this case, the approaching object has a positive Doppler frequency shift of the main echo signal equal to ω _ℓ = 90 Hz, and Doppler frequency shifts of the additional echo signals are ω _k = -185 Hz and ω _m = 365 Hz. The delays of the main and additional echo signals coincide and are equal to τ _pk = τ _pℓ = τ _pm = 2 μs. In a stationary object, the Doppler frequency shift of the main echo signal is zero, and the Doppler frequency shifts of the additional echo signals are equal to ω _k = -280 Hz and ω _m = 280 Hz. The delays of the main and additional echo signals coincide and are equal to τ _pk = τ _pℓ = π _pm = 1 μs;

- the value of the modulus of the Doppler frequency shift | ωℓ | the main echo signal of each selected signal and a decision is made on the presence of a moving object for | ω _ℓ |> Δ _ω and a stationary object for | ω _ℓ | ≤Δ _ω .

The threshold Δ _ω is chosen based on minimization of the probability of error in determining the type of object.

,

и составляющих k_npk, k_npm комплексных частотно-временных изображений отобранных сигналов каждого неподвижного объекта

. При превышении порога принимается решение об объединении отобранных сигналов. Порог по корреляции ρ выбирается исходя из минимизации вероятности ложной тревоги, а ()* - означает комплексное сопряжение.At the second stage, the cross-correlation coefficients of the components k _npℓ , k _npk , k _{npm of the} complex time-frequency images of the selected signals of each moving object are compared with the threshold ρ

,

and constituents k _npk , k _{npm of} complex time-frequency images of the selected signals of each fixed object

. If the threshold is exceeded, a decision is made to combine the selected signals. The correlation threshold ρ is selected based on minimizing the probability of false alarm, and () * - means complex conjugation.

The difference between the operations of checking the correlation level of the components of complex FWM signals of moving and stationary objects is due to the fact that, as noted earlier, a fixed object is characterized by an equal or close to zero value of the Doppler frequency shift ω _{ℓ of the} main Doppler echo signal from the body of the object (component k _npℓ ) and, as a result, its essential masking by the direct signal of the backlight transmitter and reflections from other stationary large objects. In this regard, for a stationary object, the correlation of the components k _npℓ with the components k _npk and k _{npm is} not very informative.

Note that at this stage it was possible to preliminarily find from the AFR described by the values of the components k _npℓ , k _npk , k _npm , the directions of arrival of the compared signals and to combine the signals coming from one direction. However, the operations of generating and comparing with the threshold of coefficients of mutual correlation of AFRs require significantly lower computational costs compared with operations to determine the directions of arrival of the compared signals and, as a result, significantly increase the speed of this stage of signal processing [4].

2) each combined multi-frequency signal with a symmetric spectrum is identified as an echo of the Doppler signature of the detected object.

Note that the described signal processing operations can be considered as recognition and selection operations of useful target echoes against a background of interference, the effectiveness of which is illustrated in FIG. 3.

From FIG. 3b it can be seen that, in contrast to the prototype method (Fig. 3a), the proposed method provides recognition and selection of useful echo signals of the Doppler signature of the object against the background of an intense stream of noise and interference, which significantly increases the probability of detection of radio-silent objects and makes it possible their subsequent classification.

To perform subsequent operations, the identified echo signals of the Doppler signature of moving and stationary objects are fixed together with their parameters (components k _npℓ , k _npk , k _npm , as well as the values of the Doppler frequency shift ω _{ℓ of the} main Doppler echo signal, the values of Doppler frequency shifts ω _k , ω _{m of} additional echo signals and their time delays τ _pℓ , τ _pk , τ _pm ).

Note that the described operations of recognition and selection of useful echo signals of targets against the background of interference are key when increasing the probability of detection and providing the ability to classify a wide class of radio-silent objects;

3) the echo-signals of the Doppler signature of the detected object determines the azimuthal elevation direction, spatial coordinates, bistatic velocity and its classification is carried out.

When determining the azimuthal elevation directions of arrival, for example, using the known method [3] using the identified echo signals of the Doppler signature of objects (signals k _npℓ in the case of a moving object and signals k _npk and k _npm in the case of a stationary object), a complex two-dimensional angular spectrum is synthesized , the maximum modulus of which determines the azimuthal elevation direction of arrival (α, β) of the scattered signal of the detected object, where α is the azimuth and β is the elevation angle.

After that, the spatial coordinates of each detected object are determined by known methods according to the found azimuthal elevation directions of arrival and time delays [4].

The bistatic speed is determined by the formula ϑ _b = λω _ℓ / 2, where λ is the wavelength of the backlight radio signal. For the one shown in FIG. In case 2a, we have ω _ℓ = 90 Hz. At λ = 0.5 m, we obtain ϑ _b = 0.5 · 90/2 = 22.5 m / s = 81 km / h.

When classifying detected objects in device 4-2, the following actions are performed:

- they compare with the threshold values of the elevation direction of arrival β of the echo signal of the Doppler signature of each detected stationary object and decisions are made about the presence of:

air stationary (hanging) object with β> Δ _β ;

ground stationary object with β≤Δ _β ;

- the values of the elevation direction of arrival β of the echo signal of the Doppler signature of each detected moving object are compared with the threshold and decisions are made on the presence of:

air moving object with β> Δ _β ;

ground moving object with β≤Δ _β .

Thresholds Δβ Δ _ω and selected based on minimizing the probability of error in determining the type of object;

- echo signals of the Doppler signature of mobile air and ground objects are converted into echo signals with a zero value of the Doppler frequency shift ω _{ℓ of the} main echo signal from the object’s body.

The conversion is carried out by shifting the Doppler signature of each detected moving object to the echo frequency of the echo signal. At the same time, the Doppler shift ω _{ℓ of the} main echo signal from the object’s body, which is not informative at the next stage of classification, is compensated, and it is possible to classify objects according to echo signals of a Microdoppler signature containing unique information about the type of each detected object.

For the one shown in FIG. In case 2a, the magnitude of the Doppler shift of the main echo signal from the body of the object, which must be compensated, is equal to ω _ℓ = 90 Hz.

Note that for motionless objects, this operation is not necessary, since they are characterized by a zero value of the Doppler shift ω _{ℓ of the} main echo signal from the body of the object. Consequently, the identified echoes of the Doppler signature of stationary objects are actually echoes of the Microdoppler signature and already contain unique information about the type of each detected fixed object;

- the echo signals of the microdoppler signature are used to classify detected objects.

In this case, the echo signals of the microdoppler signature of the detected objects are compared with the reference echo signals of the microdoppler signature previously generated for the required classes of objects and the class of the detected object is determined from the signals with maximum coincidence.

The required classes of objects for which reference echo signals of a micro-Doppler signature are preliminarily generated, for example, can include: Yak-54 aircraft, Mi-1 helicopter, Bell 47 helicopter, Parrot AR.Drone quadrocopter, Yamal 730 amphibious boat and etc.

A comparison of the echo signals of a microdoppler signature or eigenvectors and eigenvalues obtained on their basis is carried out by known methods, for example, by a correlation method [5].

The device 5 displays the results of radio monitoring.

Thus, through the use of new operations that extract additional information about the fine structure of the electromagnetic field of the echo signals of the Doppler signature of the objects (the main Doppler echo from the body of the object and additional echo signals of the microdoppler signature of the object), it is possible to solve the problem with the achievement of the technical result .

Information sources

1. RU, patent, 2429501, cl. G01S 13/02, 2011.

2. RU, patent, 2444754 C1, cl. G01S 13/02, 2012.

3. Parkhomenko N. G., Peretyatko A. A., Reyzenkind Y. A., Onishchenko B. C., Shevchenko V. N. Application of the variational method to the problem of estimating signal parameters in passive radar with extraneous illumination // Avtometriya. 2014. 50, No. 1. S. 60-65.

4. RU, patent, 2190236, cl. G01S 5/04, 2002.

5. R. Duda, P. Hart. Pattern recognition and scene analysis. Ed. "World", M., 1976.

Claims (1)

The method of radio monitoring of radio-silent objects, which consists in choosing a radio transmitter emitting a spread spectrum signal, synchronously receiving the multipath signals including the direct signal of the transmitter and the signals of this transmitter scattered by objects from the antenna array, synchronously converting the ensemble of signals received by the antennas into digital signals from digital signals generate signals of complex frequency-time images of antennas, which determine the number of scattered signals, their Doppler frequency shifts and time delays, and also isolate the components of complex time-frequency images corresponding to the found shifts and delays, from which a vector signal of amplitude-phase distribution (AFR) of each scattered signal is generated, characterized in that the scattered signals and signals with different Doppler frequency shifts are compared but matching delays and AFR are combined into a multi-frequency signal with a symmetric spectrum, which is identified as an echo of the Doppler signature of the detected object By echo Doppler signature signals define azimuthally elevation direction, the spatial coordinates bistatic speed and performs classification of detected objects.

Images