RU1841072C - Chirp signal recognition device - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to radio engineering and is intended for operation in electronic surveillance stations. The device comprises an autocorrelator, three threshold units, two switches, two interval-to-number converters, three registers, a divider unit, a coincidence unit, an envelope detector, a comparator, a univibrator, three delay units, three threshold units and an OR element. The listed devices are connected to each other in a certain manner.

EFFECT: high probability of recognising a chirp signal.

5 dwg

Description

The proposed device for the recognition of linearly-frequency-modulated / LFM / signals is designed to work in radio intelligence stations / RTR / and in passive target designation systems / PSCU / as equipment for determining the type and parameters of intrapulse modulation of complex signals to solve problems of signal selection and identification.

As the first analogue, we consider the device according to ed. testimonial. No. 1840896 / application No. 2206387 of 07/05/1976 /, in which separate processing channels are used to distinguish phase-shift / FM / and LFM signals. Each channel contains autocorrelators, which include delay lines, multipliers, and filters. To form a sign of receiving an LFM signal, information on the bipolarity of the voltage of the beat signal at the output of the low-pass filter / low-pass filter / autocorrelator when processing the LFM signals is used here. This method of implementing a device for distinguishing chirp signals leads to the fact that when processing FM signals, the response of the autocorrelation channel of the chirp signals is also bipolar, and a false sign of receiving a chirp signal is generated at its output. To eliminate false information when processing an FM signal, a blanking circuit is used to form a sign of receiving an LFM signal, which is carried out by a sign of receiving an FM signal. However, the sensitivity of the channel for processing the LFM signal in this device is 5-7 dB higher than the sensitivity of the channel for processing FM signals due to different LPF bands at the outputs of the autocorrelators of the corresponding channels / the band of the LPF of the channel for processing the FM signal is much larger than the band of the LPF of the channel for processing the LFM signal /. Different sensitivity of the channels leads to the fact that the FM signals in the dynamic range are 5-7 dB higher than the sensitivity level of the processing channel of the LFM signal are taken as LFM signals, because in this range, the channel for processing the FM signals does not work and the channeling of the channel for processing the chirp signal is not performed. Therefore, in this dynamic range, the device has a low reliability of distinguishing signals by the output of "chirp".

As a second analogue, we consider a device in which, to increase the reliability of distinguishing chirp signals, an algorithm is used to equality the time intervals between zero transitions of the autocorrelator response to chirp signals. The formation of the sign of receiving the LFM signal is produced here after a sequential comparison of each current interval between adjacent pulses by the zero-junction of the autocorrelator response with its previous value. Always compare two adjacent intervals, and the decision is made when three or more / are equal, depending on the required statistical reliability of distinguishing / such intervals. The time intervals between the zero transitions of the beat signal at the output of the autocorrelator on the FM signals are not the same and there is no false information at the output of the "LFM" from their influence.

As a third analogue, we consider the device according to ed. testimonial. No. 1841019 / application No. 3112397 dated 04/12/1985 /, in which the algorithm for equality of time intervals between impulses of zero-transitions of the autocorrelator response, considered in the description of the second analogue, is used to form the “LFM” feature. To increase the accuracy of interval comparison, an additional register is introduced here, and the register control scheme is made in such a way that the previous intervals are compared over the entire duration of the current interval between adjacent zero-transition impulses of the autocorrelator response. This leads to increased fidelity of the formation of a sign of receiving chirp signals.

As the fourth analogue, we consider a device in which the algorithm considered in the description of the second and third analogues is used to form the “LFM” feature. The advantages of this device are its high fidelity to the formation of a sign of receiving LFM signals with a wide range of changes in the parameters of their intrapulse modulation and the simplicity of technical implementation.

The considered analogs provide high reliability of the solution of the recognition problem in the class of LFM, FM, and simple signals in a large / 60-80 dB / dynamic range. Currently, the classes used in radar / radar / signals have expanded significantly. Find practical use signals with discrete frequency modulation / DFM /, which can significantly improve the ability of the radar to adapt to the jamming environment, to increase the energy and signal secrecy of its work.

In the class of LFM, DFM, FM and simple signals, known recognition devices have a low reliability of distinguishing by the output of "LFM", which is their drawback. The decrease in the reliability of the difference in the output of the "LFM" is due to the fact that in known devices for distinguishing LFM signals, only information on the equality of time intervals between zero transitions of the autocorrelator response is used and information on the waveform of the beats between zero transitions is not used. When receiving DFM signals, known devices can form erroneous decisions on the receipt of ChF signals, for example, when the following conditions are met:

Δω _n · τ _s = π · n

where Δω _n is the n-th discrete frequency of the frequency response signal;

τ _s - the duration of deposits in the circuit of the autocorrelator;

n = 0, 1, 2 ... is the discrete number.

In the case of equal durations of the frequency samples of the analyzed DFM signal when this condition is fulfilled, the intervals between the zero-transitions of the beat signal at the output of the autocorrelator will be the same and the known devices form a false sign "LFM" when processing the DFM signals.

The proposed technical solution is aimed at eliminating the above drawback, i.e. to increase the reliability of distinguishing chirp signals.

As a prototype, we select a device, which of the considered analogues is closest in technical essence to the proposed device.

In FIG. 1 shows a block diagram of a prototype.

The prototype contains an autocorrelator 1, an envelope detector 2, a threshold block 3, a comparator 4, a key 5, a single vibrator 6, a delay element 7, an interval-code converter 8, registers 9, 10, a divider 11, a delay element 12, a threshold block 13, register 14 and match block 15.

Autocorrelator 1, the input of which is connected to the input of the envelope detector 2 and is the device input, threshold block 3, key 5, interval-code converter 8, register 9, divider 11, threshold block 13, register 14 and match block 15, the output of which is the output of the device, connected in series. The output of the key 5 is also connected to the input of the delay element 7 and the control input of the register 10, the output and signal input of which are connected, respectively, with the second input of the divider 11 and the output of the register 9, the control input of which is connected to the output of the delay element 7 and through the delay element 12 with the control input of the register 14. The output of the envelope detector 2 through the comparator 4 is connected to the control input of the key 5 and to the input of the one-shot 6, the output of which is connected to the reset inputs of the interval-code converter 8 and registers 9, 10, 14.

As mentioned above, the disadvantage of the prototype is the low reliability of distinguishing chirp signals in the processing of subfrequency signals, because at the same time, a false sign of receiving "LFM" is formed. This leads to a decrease in the quality of solving problems of selection and identification of signals, the probability of correct recognition of radar types and their carriers, and the effectiveness of radio countermeasures systems.

The aim of the present invention is to increase the reliability of distinguishing chirp signals in the processing of chirp signals.

This is achieved by the fact that in a known device containing a series-connected autocorrelator, a first threshold block, a key, an interval-code converter and a register, a division block, a second threshold block, a second register and a coincidence block, the output of which is the output of the device, and the first delay element, the input and output of which are connected respectively to the output of the first key and to the control input of the first register, the second delay element, the input and output of which is connected to the control inputs of the first and w of registers, a third register, the output of which is connected to the second input of the division unit, and a series-connected envelope detector, the input of which is combined with the input of the autocorrelator and is the input of the device, a comparator and a one-shot, the input and output of which are connected respectively to the control input of the first key and the combined reset the inputs of the interval-code converter and three registers, the third delay element and the third threshold block are connected in series, the input of which is connected to the second output of the car a correlator, a second key, the control input of which is connected to the output of the comparator, an OR element, the second input of which is connected to the output of the first key, and a second interval-code converter, the output and fault input of which are connected, respectively, with the signal and fault inputs of the third register, the control input of which is connected to the output of the third delay element, the input of which is connected to the output of the OR element.

Such a solution provides an increase in the reliability of distinguishing LFM signals when processing signals with DFM. New elements / the third threshold block, the second key, the OR element, the second interval-code converter, the third delay element / and the connections between them allow to exclude the formation of a false indicator "LFM" when processing signals with DFM, which increases the reliability of distinguishing signals.

The authors are not aware of technical solutions having features that match the distinctive features of the proposed technical solution. It should be noted that the proposed device includes without exception all elements of the prototype, saves their names and most of the links, however, the breaks in the connections between the inputs of the register 10 / cm. FIG. 1 / and other elements of the prototype taking place in the proposed device compared to the prototype / in the proposed device, the signal input of the first register is connected not to the output of the second register, but to the output of the entered second interval-code converter, and the control input of the first register is not connected to the output of the first key, and to the output of the introduced delay element /, it is not possible to consider the proposed device as an additional invention, because it does not contain, without exception, the totality of the features of the prototype.

In FIG. 2 shows a block diagram of the proposed device.

The device includes an autocorrelator 1, envelope detector 2, threshold blocks 3, 4, comparator 5, keys 6, 7, one-shot 8, OR element 9, delay element 10, interval-code converters 11, 12, delay element 13, registers 14 , 15, divider 16, delay element 17, threshold block 18, register 19, and coincidence block 20.

The inputs of the autocorrelator 1 and the envelope detector 2 are connected together and are the input of the device. The autocorrelator 1 is made according to known quadrature schemes / see, for example, FIG. 3 / and has two outputs of the quadrature components of the beat signal. The first output of the autocorrelator is connected to the input of the threshold block 3 and then through the key 6, the interval-code converter 11, register 14, the divider 16, the threshold block 18 and the register 19 is connected to the input of the match block 20, the output of which is the output of the device. Between the signal input of the interval-code converter 11 and the control input of the register 14, as well as between the control inputs of the registers 14 and 19, delay elements 10 and 17 are included, respectively. The second output of the autocorrelator 1 is connected to the input of the threshold block 4 and then through key 7, an element OR 9, the second input of which is connected to the output of the key 6, the interval-code converter 12 and the register 15 is connected to the second input of the divider 16. A delay element 13 is connected between the signal input of the interval-code converter 12 and the control input of the register 15. Output de envelope vector 2 through a comparator 5 is connected to the control inputs of the keys 6, 7 and the input of a single-shot 8, the output of which is connected to the reset inputs of the interval-code converters 11, 12 and registers 14, 15, 19.

Consider the operation of the proposed device. For clarity, we use stress plots at various points of the block diagram depicted in FIG. four.

It is known that when the LFM signal is input to the autocorrelator input / Fig. 4a, its response is harmonic oscillation with a constant frequency, while the outputs of the quadrature components of the beat signal of the autocorrelator 1 will have the same harmonic oscillations, 90 ° shifted in phase relative to each other / Fig. 4, b, c /. From the outputs of the threshold blocks 3, 4, short pulses of zero transitions, the temporary position of which corresponds to the transitions through zero of the beat signal at the outputs of the autocorrelator / Fig. 4d, d /, are supplied to the keys 6, 7, which are controlled by the strobe from the output of the comparator 5. The strobe is formed by the envelope detector 2 when a signal is detected and normalized by the comparator 5 / Fig. 4, e /. Thus, the outputs of the keys 6, 7 pulses of zero-transitions will be present only if there is a signal at the input of the device.

From the output of the key 6 pulses of zero transitions / Fig. 4, g / arrive at the interval-to-code converter 11, where the values of time intervals between adjacent pulses are converted to code. The obtained value of the time interval is recorded in register 14, the output of which is input to the divider 16.

From the output of the key 7 pulses of zero transitions / Fig. 4, d / enter the input of the OR element 9, the second input of which receives pulses of zero transitions from the output of the key 6 / Fig. 4, g /. Through the element OR 9 pulses of zero transitions from the keys 6, 7 / Fig. 4, w / enter the interval-to-code converter 12, where the value of time intervals between adjacent pulses is converted to code. The obtained value of the time interval is recorded in the register 15, the output of which is fed to the second input of the divider 16. The time interval codes between adjacent pulses of zero transitions are recorded in the registers 14, 15 by the pulses of zero transitions through delay elements 10, 13, which are intended for recording the current interval between adjacent pulses into the corresponding registers after the end of the conversion of the interval into a code in the interval-to-code converters 11, 12. The delay time here is selected from the condition:

T _etc. ≤τ _P1 <τ _o

where τ _z1 - the delay time of the delay elements 10, 13;

τ _CR - the duration of the operation of converting the interval into the code of converters 11, 12;

τ _about - the duration of the pulses of zero transitions.

Conditions τ _P1 ≥τ _etc. need to record current values of intervals between adjacent pulses codes into the registers 14, 15 are performed after the conversion length of the time interval in the code converters 11, 12, and the condition _P1 τ <τ _{of the} necessary codes to record current intervals was carried out in the corresponding registers before the measurement of the new intervals by the converter.

It was indicated above that when processing the chirp of the beat signal at the quadrature outputs of the autocorrelator / Fig. 4b, c / are harmonic oscillations with a constant frequency, 90 ° out of phase with respect to each other. In this case, the time intervals between adjacent pulses of zero-transitions of the beat signals are equal to each other, and the time intervals between adjacent pulses at the output of the key 6 / Fig. 4, g / two times the time intervals between adjacent pulses at the output of the element OR 9 / Fig. 4, w /. These processing features are used in this device to recognize chirp signals.

In register 14, the value of the current interval between adjacent zero-transition pulses is stored at the output of the key 6, and in register 15, at the output of the OR 9 element. Into dividers 16, the values of the intervals are compared. The comparison result is tested at a threshold in threshold block 18. If the interval code recorded in register 14 is exceeded by the interval code recorded in register 15, the logic unit is formed twice at the output of threshold block 16. Otherwise, a logical zero.

The result of comparing the intervals of the output of the threshold block 18 is sequentially recorded in the shift register 19 by pulses of zero transitions, which are received at the control input of the register through the delay element 17, the delay duration of which is selected from the condition:

τ _s2 ≥t _Wed + t _en

where τ _z2 - the delay time of the delay element 17;

t _cf - the duration of the operation of comparing codes in the divider 16;

t _en - the duration of the operation of the analysis of the comparison result in the threshold block 18.

From the output of the shift register 19, successively recorded results of the comparison of neighboring intervals are fed to the input of the coincidence unit 20, the output of which forms a sign of receiving the LFM signal in the presence of three or more units in a row in the cells of the shift register 19, which corresponds to the equality of three or more / depending on the required statistical reliability of the difference / successive time intervals between the pulses of zero transitions at the output of the key 6 and the excess of the duration of the intervals between adjacent pulses of zero transitions on the output of the key 6 over the duration of the intervals on the output of the element OR 9 twice.

After the end of the strobe pulse, the output of the comparator 5 starts a single-shot 8, from the output of which the trailing edge of the pulse / Fig. 4, and / the interval-code converters 11, 12 and the registers 14, 15, 19 are reset. The device is again prepared for analyzing the input signals.

When processing the DFM signal (Fig. 5, a), the beats at the quadrature outputs of the autocorrelator are voltages proportional to the phase incursion at the outputs of the autocorrelator. Within the discrete frequency of the DFM signal, the amplitude of the beat signal is constant. The change in the amplitude of the beat signal occurs at the moment of changing the frequency of the DFM signal simultaneously at two quadrature outputs.

This can be explained as follows.

It is known that the beat signal V _b at the output of the autocorrelator when exposed to a constant frequency signal at its input is:

V _b = V _o · cos (ω _o τ _s )

where V _o , ω _o - the amplitude and frequency of the signal at the input of the autocorrelator.

When exposed to the input of the autocorrelation of the DFM signal, the beat signal will look like:

V _bDFM = V _o · cos [(ω _o + Δω _n ) · τ _s ] = V _o [cos (ω _o τ _s ) · cos (Δω _n · τ _s ) -sin (ω _o τ _s ) · sin ( Δω _n · τ _s )]

where Δω _n is the change in the frequency of the discrete DFM signal.

We take V cos (ω _o · τ _s ) = 1, then

V _bDFM = V _o · cos (Δω _n · τ _s )

At the second quadrature output of the autocorrelator, the beat signal will be:

V _bDFM = V _o · sin (Δω _n · τ _s )

From the last two expressions it is seen that the change in the amplitude of the beat signal occurs simultaneously at the two quadrature outputs of the autocorrelator at the time of changing the sampling frequency Δω _{n of the} DFM signal / Fig. 5, b, c /.

In the case of equality of the durations of the discrepancies of the frequency of the DFM signal, the intervals between the pulses of the zero transitions of the beat signal at the output of the autocorrelator will be the same. Pulses of zero transitions from the outputs of threshold blocks 3, 4 / Fig. 5d, d / d coincide in time, therefore, from the output of the OR element 9 / Fig. 5, w / to the input of the interval-code converter 12, zero-transition pulses will arrive simultaneously with zero-transition pulses to the input of the interval-code 11 converter. Codes of identical intervals will be recorded in registers 14, 15, so threshold unit 18 does not work and the device does not generate a false sign "LFM" when processing an FFM signal.

All nodes of the proposed device are made according to well-known standard schemes of modern analog and digital technology using microcircuits of series 100, 530, 556.

The quadrature autocorrelator 1 can be performed, for example, according to the circuit shown in FIG. 3. Here, the quadrature autocorrelator contains a delay element 1, a multiplier 2, a broadband quadrature directional coupler 3, a multiplier 4, and low-pass filters 5, 6. The principle of operation of such an autocorrelator does not require explanation.

Using the proposed device in RTR and PSTSU stations allows to improve the quality of solving problems of selection and identification of signals, increase the likelihood of recognizing the type of radar and its carrier, and improve the organization of effective radio response.

Claims (1)

A device for recognition of linearly-frequency-modulated signals, containing a series-connected autocorrelator, a first threshold block, a first key, a first interval code converter and a first register, a division block, a second threshold block, a second register and a coincidence block, connected in series with the envelope detector , a comparator and a one-shot, a third register, and the input of the first delay unit is connected to the output of the first key, the output is with the control input of the first register, the input of the second delay unit is connected to the control the input of the first register, the output is with the control input of the second register, the output of the third register is connected to the second input of the division unit, the output of the comparator is connected to the second input of the first key, the output of the one-shot is connected to the reset inputs of the interval-code converter, the first, second and third registers, the input of the autocorrelator and the input of the envelope detector are the input of the device for recognition of linear-frequency-modulated signals, the output of which is the output of the matching circuit, characterized in that, for the purpose of to increase the recognition probability of linearly-frequency-modulated signals, a third threshold block, a second key, an OR element and a second interval-code converter, a third delay block are introduced in series with the input of the third threshold block connected to the second output of the autocorrelator, the second input the second key is connected to the output of the comparator, the second input of the OR element is connected to the output of the first key, the reset input of the second interval-code converter is connected to the output of the one-shot, the output to the signal the input of the third register, the input of the third delay unit is connected to the output of the OR element, the output to the control input of the third register.

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