RU2472176C1 - Method for passive detection of air objects - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: result is achieved due to application of operations of 2D compression and 2D correlation filtration of received radio signals, which provides for 2D rejection of a powerful direct radio signal of a highlight transmitter, being a coherent noise that masks weak scattered radio signals, and as a result opens the possibility of detection and spatial localisation of objects with a low radial motion speed.

EFFECT: invention provides for the possibility of detecting objects with a low radial speed.

2 dwg

Description

The invention relates to radio engineering and can be used in airspace control systems using direct and dispersed radio objects 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 airborne objects is limited by significant a priori uncertainty in size, spatial orientation, reflecting properties and parameters of the movement of objects, as well as the imperfection of known methods for detecting and tracking airborne objects.

A technology for passive detection and tracking of objects using natural radio illumination of aerial targets created at a variety of frequencies by radio emissions from various transmitters in the short, meter, decimeter and centimeter wavelengths: broadcast (commercial FM broadcasting, high-definition television), information (communication) and measuring (control, navigation), has not yet received sufficient distribution, despite the fact that it can significantly increase the secrecy and effectiveness of detection, spatial localization and identification of a wide class of moving objects.

The received radio signal, as a rule, includes powerful direct radio signals and the signal components of the selected target radio illumination transmitter scattered from the earth's infrastructure. In addition, it contains time-delayed and shifted by the frequency of the Doppler shift signals scattered by objects, as well as signals of other uncontrolled sources operating at a frequency that matches the frequency of reception. For the effective detection and accurate spatial localization of a wide class of objects (cars, ships, planes and unmanned aerial vehicles, helicopters, rockets, descent vehicles), high-quality selection of weak radio signals scattered from objects against the background of a powerful direct signal of the selected radio backlight transmitter, as well as against the background of signals other unwanted sources. In most typical situations, the noise level is 40-60 dB higher than the level of scattered signals.

There is a method of passive detection of airborne objects [1], which consists in selecting transmitters that emit spread-spectrum radio signals, synchronously receiving an array of multipath radio signals including direct radio transmitters and scattered radio signals from these transmitters, synchronously transform 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 determined time delays, Doppler shifts and directions of arrival of scattered signals, according to time delays, Doppler shifts and directions of arrival, they perform the detection and spatial localization of airborne objects.

The disadvantage of this method is the limited detection range of airborne objects due to the lack of operations to compensate for coherent interference arising from the leakage of the direct radio signal of the backlight transmitter into the reception channel of the radio signals scattered by the objects.

More effective is the method of passive detection of airborne objects [2], free from this drawback and selected as a prototype. According to this method:

receive two spatially combined receiving channels direct radio signal from the backlight transmitter and the radio signal scattered from the object;

synchronously convert the received radio signals into complex digital signals, which are synchronously recorded on a given time interval;

from complex digital signals form a signal of a complex cross-correlation function, depending on the frequency shift of the received signals;

exclude the central part of the complex cross-correlation function and receive a signal of the modified complex cross-correlation function;

converting the signal of the modified complex cross-correlation function into a modified scattered complex digital signal;

generating a signal depending on the time and frequency shifts of the complex two-dimensional cross-correlation function between the modified scattered complex digital signal and the direct complex digital signal;

compressed scattered signals are extracted from the signal of the complex two-dimensional cross-correlation function and their parameters are determined, which are used for the detection and spatial localization of objects.

The prototype method includes the operation of compensating for coherent interference arising from the leakage of the direct radio signal of the backlight transmitter into the reception channel of the radio signals scattered by the objects. Moreover, the prototype method compresses the spectrum of a powerful direct radio signal and its subsequent rejection in the frequency domain, thereby increasing the signal-to-noise ratio of the received weak scattered radio signal. However, such a one-dimensional rejection removes all scattered radio signals with small values of the Doppler frequency shift at all possible detection ranges, that is, makes it impossible to detect objects with a low radial speed.

Thus, the disadvantage of the prototype method is the inability to detect objects with low radial speed.

The technical result of the invention is the ability to detect objects with low radial velocity.

The ability to detect objects with a low radial speed is achieved by:

- the application of the operations of forming a two-dimensional cross-correlation function, depending on the time and frequency shifts of the received signals, instead of a one-dimensional cross-correlation function, depending only on the frequency shift of the received signals;

- use instead of one-dimensional correlation filtering of two-dimensional correlation filtering operations of the received signals, which provide the rejection of a powerful direct radio signal of the illumination transmitter, which is a coherent interference, masking weak radio signals scattered by airborne objects.

The technical result is achieved by the fact that in the method of passive detection of air objects, which consists in the fact that the direct radio signal from the backlight transmitter and the radio signal scattered by the air object are coherently received by two spatially aligned receiving channels, the received radio signals are simultaneously converted into complex digital signals that are synchronously recorded at a given time interval, according to the invention from complex digital signals form a signal depending on the time and frequency s of the engines of the complex two-dimensional cross-correlation function (DCF), exclude the central part of the complex DCF and obtain the signal of the modified complex DCF, from the signal of the modified complex DCF and the direct complex digital signal form the modified scattered complex digital signal, form the resulting signal of the complex DCF between the modified diffused complex digital signal and a direct complex digital signal, from the resulting signal of the integrated DVKF emit compressed e scattered signals and determine their parameters, which are used for the detection and spatial localization of air objects.

The operation of the method is illustrated by drawings:

Figure 1. Block diagram of a device that implements the proposed method for passive detection of airborne objects;

Figure 2. The operation diagram of a device that implements the proposed method.

The device (figure 1), which implements the proposed method, contains a series-connected system for receiving and pre-processing 1, a system for modeling and selection of radio transmitters (RPD) 2 and a computer system 3.

In turn, the reception and pre-processing system 1 includes a direct radio signal reception channel including an antenna system (AS) 1-1, a frequency converter 1-2, an ADC 1-3, and a scattered radio signal reception channel including an ADC 1-4, a converter frequencies 1-5 and AC 1-6.

Computing system 3 includes an interference compensation device 3-1, a signal shaper of the resulting DCF 3-2 and a device for detecting and localizing objects 3-3.

In this case, the system 2 is connected to the input of the device 3-3, and also has an interface for connecting to an external RPD base. In addition, the device 3 has an output intended for connection to external systems.

Subsystem 1 is an analog-to-digital device and is designed to receive direct radio signals using directional AC 1-1 and to receive scattered objects by radio signals using directional AC 1-2, as well as to convert received radio signals to complex digital signals.

Note that after the synchronization parameters of the direct radio signal of the selected backlight transmitter are measured or when they are a priori known, the direct radio signal of the transmitter can be generated by modeling in system 2.

Frequency converters 1-2 and 1-5 are made with a common local oscillator and with the bandwidth of each channel, variable in accordance with the width of the spectrum of the received radio signal. A common local oscillator provides two-channel coherent signal reception. ADC 1-3 and ADC 1-6 are also synchronized by the signal of one reference oscillator (to simplify the local oscillator and the reference oscillator are not shown in the diagram).

Subsystem 2 is a computing device and is designed to identify, select, and periodically update spread spectrum radio transmitters used to illuminate a given area of airspace, as well as to generate model signals of selected transmitters.

Computing system 3 is designed to compensate for coherent interference due to leakage of the direct radio signal of the backlight transmitter into the channel for receiving radio signals scattered by objects (device 3-1), generating a signal of the resulting integrated DCF and identification of compressed scattered signals (device 3-2), detection and generation spatial coordinates of airborne objects (device 3-3).

Thus, the composition of the device that implements the proposed method allows us to solve two main problems: the problem of choosing RPD - radio illumination sources that provide acceptable characteristics of exposure to airborne objects and the problem of suppressing the direct radio signal, which exceeds the useful radio signal by 40-60 dB.

An enlarged diagram of the functioning of the device that implements the proposed method for passive detection of airborne objects is presented in figure 2.

The circuit includes an RPD transmitter with a known location, emitting a spread spectrum radio signal, and also a detection-direction finding (SOP) station. The radio signal of the RPD transmitter is propagated by an earth or surface wave, which in the form of a direct (reference) radio signal is received by the channel for receiving the direct radio signal of the SOP. In addition, the radio signal of the RPD transmitter is propagated by a wave irradiating a given area of air space and received by the SOP in the form of a radio signal scattered by an air object and in the form of a direct radio signal, which is coherent interference with a weak radio signal scattered by an air object.

The object is characterized by the modulus V _c of the velocity vector, the angle φ between the object velocity vector and the bistatic angle bisector, the value of the bistatic angle θ, as well as the distance r ₁ from the RPD radio illumination transmitter to the object, the distance r _c from the object to the SOP receiving antenna, and the distance d from the transmitter RPS radio illumination to SOP.

The RPD transmitter can conditionally be assigned to one of the classes: uncontrolled (uncontrolled) and controlled (managed). For example, if the RPD transmitter was not specifically created to work together with a detection-direction finding station and does not have communication lines with a detection-direction finding station, it can be considered as uncontrolled (uncontrolled). Uncontrolled transmitters can be any systems or devices emitting in the ranges of short, meter, decimeter and centimeter waves extended-spectrum radio signals and satisfying the following requirements: spatial position should provide direct visibility between the transmitter and the detection system (if the parameters of the radio signal with accuracy before synchronization is a priori known, then direct visibility between the transmitter and the detection system is not required); the frequency and power of the emitted radio signal should provide effective detection of a wide class of airborne objects. An example of uncontrolled transmitters can be transmitters of communication, information and measuring radio systems for various purposes. If the RPD transmitter is specially designed to solve the problem of detecting airborne objects together with a detection-direction finding station, then this transmitter can be classified as controlled (controlled). Moreover, to control the operating modes of the RPD transmitter, a communication line with a detection-direction finding station is provided.

The device operates as follows.

In system 2, on the basis of data from an external database of backlight transmitters using modeling software, a set of transmitters emitting spread-spectrum radio signals is identified, selected and periodically updated. In the simulation, possible coverage areas, detection probabilities, and achievable localization and identification accuracy of airborne objects of various classes, which can be provided with different types of placement of transmitters relative to the detection-direction finding station, are estimated. In addition, in system 2, received direct radio signals are regenerated or model transmitter signals are generated with the required synchronization parameters.

The parameters of the selected transmitter (number, carrier frequency, spectrum width, shape, synchronization parameters and power of the emitted signal, coordinates or distance and angular position relative to the SOP) are stored in subsystem 2, fed to device 3-3, and also used to configure frequency converters 1 -2 and 1-5. In order to simplify the control circuit of the frequency converters 1-2 and 1-5 are not shown.

According to the signals of system 2, AC 1-1 is directed to a given azimuthal elevation direction of receiving a direct signal of the selected RPD, AC 1-2 is directed to a given azimuthal elevation direction of receiving a scattered radio signal, and frequency converters 1-2 and 1-5 are tuned to a given frequency receiving f _k . The direct radio signal x ₁ (t) of the selected spread spectrum transmitter and the airborne radio signal x ₂ (t) of this transmitter are coherently received at a frequency f _{k by} two spatially aligned receiving channels.

Received AC 1-1 time-dependent direct radio signal x ₁ (t), as well as received AC 1-6 time-dependent t scattered radio signal x ₂ (t) is transferred to a lower frequency in frequency converters 1-2 and 1-5 respectively.

и в рассеянный комплексный цифровой сигнал

, где z - номер временного отсчета сигнала. Комплексные цифровые сигналы

и

совместно со значением азимутально-угломестного направления приема (α, β) рассеянных радиосигналов поступают в устройство компенсации помех 3-1, где синхронно регистрируются на заданном временном интервале.The radio signals x ₁ (t) and x ₂ (t) formed in the frequency converters 1-2 and 1-5 are synchronously converted using ADC 1-3 and ADC 1-4 into a direct complex digital signal

and into a scattered complex digital signal

where z is the time reference number of the signal. Integrated Digital Signals

and

Together with the value of the azimuthal elevation direction (α, β) of the scattered radio signals, they arrive at the interference compensation device 3-1, where they are synchronously recorded for a given time interval.

In addition, in the device 3-1, the following actions are performed:

и

формируется сигнал, зависящий от временного τ и частотного F сдвигов комплексной ДВКФ

;- from complex digital signals

and

a signal is formed depending on the time τ and frequency F shifts of the complex DCF

;

и получается сигнал модифицированной комплексной ДВКФ

;- excludes the central part of the integrated FEFF

and the signal is obtained from a modified integrated DCF

;

и прямого комплексного цифрового сигнала

формируется модифицированный рассеянный комплексный цифровой сигнал

.- from the signal of the modified integrated DCF

and direct complex digital signal

a modified scattered complex digital signal is generated

.

выполняются следующие действия:When generating a modified scattered complex digital signal

The following actions are performed:

для получения сигнала

;a) the signal values of the modified integrated DCF are summed

to receive a signal

;

и получается сигнал

, где

- оператор обратного ДПФ;b) the inverse discrete Fourier transform (DFT) of the signal is performed

and you get a signal

where

- operator of the inverse DFT;

умножается на комплексно сопряженный цифровой прямой сигнал

и получается модифицированный рассеянный комплексный цифровой сигнал

, где * - обозначает комплексное сопряжение.c) the found signal

multiplied by a complex conjugate digital direct signal

and you get a modified diffuse complex digital signal

where * - denotes complex conjugation.

осуществляется по формуле

. Этот способ обеспечивает более высокую устойчивость к амплитудным флуктуациям сигналов.Another method is possible in which the formation of a modified scattered complex digital signal

carried out by the formula

. This method provides higher resistance to amplitude fluctuations of the signals.

The described operations are key in achieving the specified technical result, since instead of the one-dimensional compression of a powerful direct radio signal (coherent interference) only in frequency, it is two-dimensional compressed in time and frequency, as well as the subsequent two-dimensional rejection of the compressed signal in the time-frequency domain. This provides an increase in the signal-to-noise ratio of the received weak scattered radio signal. In this case, the received scattered radio signals with small values of the Doppler frequency shift at all possible detection ranges are stored, which makes it possible to detect objects with a low radial speed;

совместно с прямым комплексным цифровым сигналом

и значением азимутально-угломестного направления приема (α, β) рассеянного радиосигнала поступают в формирователь результирующего сигнала ДВКФ 3-2.Received modified scattered complex digital signal

in conjunction with a direct complex digital signal

and the value of the azimuthal elevation direction of reception (α, β) of the scattered radio signal is supplied to the resultant signal shaper DVKF 3-2.

In the shaper of the resulting signal DVKF 3-2 the following actions are performed:

между модифицированным рассеянным комплексным цифровым сигналом

и прямым комплексным цифровым сигналом

;- the resulting signal of the integrated DCF is formed

between the modified scattered complex digital signal

and direct complex digital signal

;

выделяются сжатые рассеянные сигналы и определяются их параметры, которые используются для обнаружения и пространственной локализации воздушных объектов.- from the resulting signal of the integrated DCF

compressed scattered signals are extracted and their parameters are determined, which are used for the detection and spatial localization of airborne objects.

The following actions are performed:

результирующего сигнала комплексной ДВКФ определяется число сжатых рассеянных сигналов, а также значения задержки по времени τ_ξ и абсолютного доплеровского сдвига F_ξ каждого ξ-го сжатого рассеянного сигнала.- modulo

the resultant signal of a complex DKVF determines the number of compressed scattered signals, as well as the time delay τ _ξ and the absolute Doppler shift F _{ξ of} each ξth compressed scattered signal.

The values of the time delay τ _ξ , the absolute Doppler shift F _{ξ of} each ξ-th compressed scattered signal and the value of the azimuth-elevation direction of reception (α, β) of the scattered signals are received in the device 3-3.

In the device 3-3, the detection and spatial coordinates of airborne objects are performed by the values of the delay τ _ξ , the absolute Doppler shift F _ξ and the azimuthal elevation direction (azimuth α and elevation angle β) of receiving the compressed scattered signals.

The following actions are performed:

- the absolute Doppler shift F _ξ and the elevation angle β of the ξth compressed scattered signal are compared with the threshold and, when the threshold is exceeded, a decision is made to detect an air object in the azimuth-elevation direction (α, β).

The threshold is selected based on minimizing the probability of missing an object;

When determining the geographical coordinates of the detected object in the device 3-3, the following actions are performed:

- the absolute distance of the signal τ _ξ determines the apparent distance to the object D = τ _ξ c, where c is the speed of light;

- the spatial coordinates of the detected object are determined by the apparent range D and the azimuth α and elevation angle β of the reception of scattered signals.

In this case, an ellipsoid of equal apparent distances corresponding to the geometrical place of points in space is constructed for the “SOP-transmitter” pair, the sum of the distances to which (from the transmitter to the object and from the object to SOP) is equal to the found value of the apparent distance D. At the intersection of the ellipsoid of equal apparent distances and the direction values (azimuth α and elevation angle β) of the scattered signals reception are determined by the geographical coordinates of the detected object.

There is another way to determine the geographical coordinates of the detected object using the angular-elliptical method. In this case, the device 3-3 performs the following actions:

- the total distance to the object r _Σc = cτ _ξ + d is calculated, where c is the speed of light;

- is the distance to the target

- the spatial coordinates of the detected object are determined by the distance to the target r _c and the azimuth α and elevation angle β of the reception of scattered signals.

, где λ - длина волны радиосигнала подсвета.In addition, the radial velocity of the target is calculated from the Doppler frequency shift of the scattered radio signal (projection of the velocity vector onto the bistatic axis, shown by a prime in FIG. 2)

where λ is the wavelength of the backlight radio signal.

The results of the detection and spatial localization of airborne objects are displayed to increase information content.

From the above description it follows that the device that implements the proposed method provides the ability to detect objects with low radial speed due to the implementation of two-dimensional processing of the received radio signals.

Thus, by using instead of one-dimensional correlation filtering operations of two-dimensional compression and two-dimensional correlation filtering of received radio signals, which provide a rejection of a powerful direct radio signal of the backlight transmitter masking weak scattered radio signals and not limiting the detection range and spatial localization of objects with a low radial speed, solve the problem with the achievement of the specified technical result.

Information sources

1. RU, patent, 2158002, cl. G01S 13/14, 2000.

2. Pat. EAPO No. 008335 by Eurasian application No. 20050110, publ. 08/29/2006 // Bulletin of the Eurasian Patent Office. - 2006. - No. 3.

Claims (1)

The method of passive detection of airborne objects, which consists in the fact that the direct radio signal from the backlight transmitter and the radio signal scattered by the airborne object are coherently received by two spatially aligned receiving channels, synchronously converting the received radio signals into complex digital signals that are synchronously recorded for a given time interval, characterized in that of complex digital signals form a signal depending on the time and frequency shifts of the complex two-dimensional mutually correlated function functions (DCF), the central part of the complex DCF is excluded and a signal of the modified complex DCF is obtained, the modified diffuse complex digital signal is formed from the signal of the modified complex DCF and the direct complex digital signal, the resultant complex DCF signal is generated between the modified diffuse complex digital signal and the direct complex digital signal, modulo the resulting signal of the integrated DCF determine the number of compressed scattered signals, a pair etram which - the value of the time delay, the absolute Doppler shift of the scattered signal each compressed value and the direction of approach elevation azimuthally receiving scattered signals - perform the detection and spatial localization air objects.

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