CN117930140A - Low-interception waveform design and processing method based on composite encryption - Google Patents
Low-interception waveform design and processing method based on composite encryption Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/50—Systems of measurement based on relative movement of target
- G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
- G01S13/589—Velocity or trajectory determination systems; Sense-of-movement determination systems measuring the velocity vector
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/28—Details of pulse systems
- G01S7/282—Transmitters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/28—Details of pulse systems
- G01S7/285—Receivers
- G01S7/292—Extracting wanted echo-signals
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/28—Details of pulse systems
- G01S7/285—Receivers
- G01S7/295—Means for transforming co-ordinates or for evaluating data, e.g. using computers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/38—Jamming means, e.g. producing false echoes
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- Radar Systems Or Details Thereof (AREA)
Abstract
The invention discloses a low-interception waveform design and processing method based on composite encryption, which is applied to the technical field of radar detection and aims at solving the problem that the existing radar emission waveform is easy to intercept by an enemy electronic jammer; the invention firstly adopts a novel encrypted waveform encrypted by pseudo-random two-phase codes, and the encrypted waveform effectively camouflage the conventional waveform by presenting chaotic parameters; then, because the encrypted signal may have a large bandwidth, a special decryption method based on local detection is provided, which is helpful to reduce the signal-to-noise ratio drop in the extended target detection to the maximum extent; and finally, completing the coherent processing within one pulse repetition time to obtain the position and speed information of the target.
Description
Technical Field
The invention belongs to the technical field of radar detection and low-interception waveform setting, and particularly relates to a radar waveform design and processing technology.
Background
With the continuous development of electronic warfare, the demand for electromagnetic environment sensing has led to the advent of a series of advanced reconnaissance technologies, and waveforms emitted by conventional radars are also increasingly easy to intercept and sort by enemy electronic reconnaissance devices, which constitutes a great threat to the viability of conventional radar systems. In recent decades, low probability of interception radars have been proposed and have become a trend in current radar designs. The low-interception probability radar can be realized through a low-interception probability wave beam design and a low-interception probability wave form design, and compared with a wave beam forming design, the low-interception probability wave form design has high universality and easy realizability, so that the low-interception probability wave form design is paid attention to.
In literature "X.Liu,T.Zhang,X.Yu,Q.Shi,G.Cui,and L.Kong,"LPI waveform design for radar system against cyclostationary analysis intercept processing,"Signal Process.,vol.201,2022", low-probability-of-interception waveform design methods are mainly divided into two categories: anti-interception and anti-recognition. The first method mainly prevents the power of the emission waveform from exceeding the detection threshold of the electronic reconnaissance equipment by reducing the power of the emission waveform, thereby realizing anti-reconnaissance and low interception probability. However, low transmit power can reduce the radar echo signal-to-noise ratio, resulting in reduced radar detection performance. Therefore, in literature "Liu Jiafang. Wideband low-interception and random-polarization radar signal model research [ D ]. University of chinese academy of sciences (national center of space science), 2019," it is mentioned that today's low-interception probability waveforms often use large time-wide product waveforms, such as LFM (LinearFrequencyModulation, chirping) and NLFM (non-linearfrequencymodulation, non-chirping), which can use lower transmit power while still having a larger signal-to-noise ratio after echo processing due to their high coherent integral gain, but these waveforms usually have regular characteristics in the time domain or frequency domain and are easily identified by electronic reconnaissance devices. The second approach achieves low probability of interception, mainly by designing waveforms in the time or frequency domain. These low-probability-of-interception waveforms consist mainly of various phase-coded waveforms, such as pseudo-random phase sequences. With the development of electronic reconnaissance technology, the traditional low-interception waveform can be identified by utilizing advanced time-frequency analysis technology.
Disclosure of Invention
Aiming at the problem that the traditional low interception probability waveform is easier to intercept, the invention provides a novel low interception radar waveform design and processing method based on composite encryption, a transmitting end encrypts a transmitted detection waveform by using a specific sequence to realize low interception, and a receiving end introduces a target detection method based on local detection to ensure detection performance.
One of the technical schemes adopted by the invention is as follows: a low interception waveform design method based on composite encryption comprises the following steps:
a1, a signal source generates an LFM signal as a pre-encryption signal;
a2, taking the pseudo-random two-phase code as an encryption sequence, and multiplying the encryption sequence by the waveform generated in the step A1 to encrypt the encryption sequence so as to form a low-interception waveform;
A3, up-converting the encrypted waveform in the step A2 and using the waveform as a radar transmitting signal.
The second technical scheme adopted by the invention is as follows: a low interception waveform processing method based on composite encryption comprises the following steps:
B1, a receiving end uses an expansion target processing method based on local detection to perform down-conversion and decryption processing on the obtained received echo signals;
and B2, performing pulse compression and moving target detection (Moving Target Detection, MTD) processing on the decrypted target echo signals, and extracting the distance and Doppler information of the target.
The invention has the beneficial effects that: firstly, encrypting a detection signal by using a pseudorandom two-phase code, wherein the encrypted signal presents chaotic parameters in a time domain and a frequency domain; then, a processing method corresponding to the encrypted waveform is provided, and a special decryption method based on local detection is provided, so that the signal-to-noise ratio reduction in the detection of the expansion target is reduced to the maximum extent; finally, completing the coherent processing within one pulse repetition time to obtain the position and speed information of the target; simulation results show that the waveform designed by the invention has low interception characteristic, and can finish the detection of the target without losing the detection performance. The decryption method based on local detection can effectively reduce the signal-to-noise ratio loss during the detection of the expansion target.
Drawings
FIG. 1 is a diagram of a radar system architecture employing complex encrypted waveforms.
Fig. 2 is a flowchart of an extended target decryption process based on local detection.
FIG. 3 is a time domain waveform and spectrum of a composite encrypted waveform according to an embodiment of the present invention;
Wherein, (a) is a time domain waveform, and (b) is a frequency spectrum.
Fig. 4 is a spectral comparison of a composite encrypted waveform and a narrowband LFM signal according to an embodiment of the present invention.
FIG. 5 is a time-frequency diagram comparison of the embodiment of the present invention with a narrowband LFM signal, reflecting the improvement of low interception performance;
Wherein, (a) is a time-frequency diagram of the present embodiment, and (b) is a time-frequency diagram of the narrowband LFM signal.
FIG. 6 is a graph comparing pulse pressure results during point target detection with a narrowband LFM signal according to an embodiment of the present invention;
The (a) is the point target detection pulse pressure result of the embodiment, and the (b) is the point target detection pulse pressure result of the narrowband LFM signal.
FIG. 7 is a graph comparing MTD results of the embodiment of the present invention with those of the narrowband LFM signal during point target detection;
Wherein, (a) is the MTD result when the point target is detected in the embodiment, and (b) is the MTD result when the point target of the narrowband LFM signal is detected.
Fig. 8 is a diagram of the detection result of the target extended by the narrowband LFM and the wideband LFM signal according to the embodiment of the present invention.
Fig. 9 is a diagram showing a comparison between an echo processing mode of a decryption method based on local detection and an echo processing result of a conventional decryption method according to an embodiment of the present invention.
Detailed Description
The present invention will be further explained below with reference to the drawings in order to facilitate understanding of technical contents of the present invention to those skilled in the art.
The main technical framework and the signal processing flow of the invention are shown in the attached figure 1, and specifically comprise two parts of contents: the transmitting end is based on the low interception waveform design process of the composite encryption, and the receiving end is based on the corresponding processing process of the received encrypted waveform;
the low interception waveform design process of the transmitting end based on the composite encryption comprises the following steps:
S1, a signal source generates an LFM signal as a pre-encryption signal;
s2, taking the pseudo-random two-phase code as an encryption sequence, and multiplying the encryption sequence by the waveform generated in the step S1 to encrypt the encryption sequence so as to form a low-interception waveform;
s3, up-converting the encrypted waveform in the step S2 and taking the waveform as a radar transmitting signal;
The processing procedure corresponding to the received encrypted waveform by the receiving end comprises the following steps:
s4, performing down-conversion and decryption processing on the obtained received echo signals by using an extended target processing method based on local detection;
s5, performing pulse compression and MTD processing on the decrypted target echo signals, and extracting the distance and Doppler information of the target.
The step S1 specifically comprises the following steps:
the S11, LFM signal can be expressed as
s(t)＝exp{jπμt2} (1)
Where T e [0, T p],TP represents the signal pulse width, μ=b/T P represents the frequency modulation slope of the LFM signal, and B is the signal bandwidth.
The step S2 specifically comprises the following sub-steps:
S21, firstly, a uniformly distributed pseudo-random sequence c (t), wherein the sequence is subjected to uniform distribution (-1, 1), and the sequence is binarized, wherein a value larger than 0 is 1, and a value smaller than or equal to 0 is-1. The binarized encryption sequence c B (t) is described in terms of chips, and can be expressed as:
Where c n denotes the nth chip of the binarized secret sequence c B (T), T c denotes the duration of each chip, and N c denotes the number of chips. g (t) represents a rectangular function, which can be expressed as
S22, any baseband signal S (t) generated by the radar signal source is expressed as a chip form
Where s n represents the nth chip of the LFM signal s (T), and T c represents the duration of each chip, consistent with the meaning and number above. Multiplying S (t) by the binarized encryption sequence c B (t) generated in step S21, resulting in an encrypted waveform d (t), which can be expressed as:
d(t)＝s(t)cB(t) (4)
The step S3 specifically comprises the following steps:
S31, assuming that the repetition time of the radar pulse is T and the carrier frequency of the transmission signal is f c, the transmission signal is expressed as
x(t)＝d(t)exp{j2πfct} (3)
The step S4 specifically comprises the following steps:
S41, firstly modeling the echo of the expansion target, assuming that M pulses are shared in a coherent processing interval, a slow-time intermediate-frequency echo model of the mth pulse received by the radar can be expressed as
Where Δt m = (m-1) T, where T is the pulse repetition time, consistent with the definition and the number set forth above, τ p-2v(t+△Tm)/c represents the delay corresponding to the mth pulse, P represents the total number of scattering points of the extended target, and a p,τp represents the scattering coefficient (including amplitude and phase) and the corresponding delay of the P-th scattering point, respectively. Assuming that the relative distance between the position of the p-th scattering point of the target and the radar is R p, the time delay of the p-th scattering point of the target relative to the radar is τ p＝2Rp/c, c is the light speed, and the speed of each scattering point is assumed to be v at the time t=0;
S42, down-converting the intermediate frequency signal r (t, m) to obtain a baseband echo signal r d (t, m), expressed as
Wherein A p′＝Apexp{j2πfcτp is a constant term; f d＝2vfc/c denotes the Doppler frequency of the target;
S43, decrypting the baseband echo signal r d (t, m) in the step S32 by using an expansion target processing method based on local detection, wherein a flow chart of the expansion target processing method of the local detection is shown in fig. 2. The radar is assumed to be in a tracking mode, so that only a distance measurement section of interest, namely a plurality of distance measurement units near a target, is required to be focused, and the division of the distance measurement units is related to the sampling rate, the signal bandwidth and the wave position, and is usually set to be the time width of a front pulse and a rear pulse of the position where the target pulse is located. The echo delay corresponding to the ranging resolution unit of the narrowband waveform is set to the size of the local detection window in the echo. At the same time, decryption is applied to each segment in the local detection window, each segment having a length equal to the pulse width.
The specific decryption process can be summarized as: firstly, determining echo delay corresponding to a distance interval of interest, and dividing a local detection window according to a range resolution unit of a narrowband waveform; then using the same c (t) traversing domain as the transmitting end to possibly be each segment of the target echo, wherein all echo segments are contained in the local detection window, and zero filling is carried out on each window before decryption so as to make the length of each window equal to the length of the local detection window; the radar is assumed to be in tracking mode, so the corresponding distance of each window where the target may be present is known. Therefore, only a few points around the peak after correlation with s (t) are taken and all peaks within the local detection window are added; and finally, carrying out threshold detection on the summation value, wherein the threshold is a sampling point near the target in the tracking mode, averaging the correlated peak values, and judging whether the target exists in the local detection window through the threshold detection.
The decrypted echo signal after threshold detection can be expressed as
Wherein t p,m＝τp-2v(t+△Tm)/c.
Simulation verification and analysis
Simulation parameters:
The narrowband LFM signal is a signal before encryption, the bandwidth b=5 MHz, the time width T p =10 μs, the sampling frequency f s =600 MHz, the pulse repetition period T r =300 μs, the carrier frequency f c =1 GHz, and the number of pulses in one CPI is 64; in the extended target scene, the bandwidth B w =200 MHz of the broadband LFM, the rest parameters are the same as the narrowband, and the energy of the broadband LFM is consistent with that of the narrowband LFM.
In the single target scene considered, the target distance is R=120 km, and the target speed is v=100 km/s; in the considered extended target scene, the number of target scattering points is 5, the scattering coefficients are 1, and the signal-to-noise ratio snr=20 dB.
The encryption sequence adopts pseudo-random two-phase codes, the code element width T B＝1/fs and the encryption coefficient is 10.
And (3) calculating a time-frequency diagram, wherein STFT is adopted, a window function is a Hanning window, the window length is 128, hopsize=4, the overlapping point number Overlap =124, and the FFT point number is 1024. Neither pulse pressure nor MTD results are windowed.
Simulation analysis:
FIG. 3 is a time domain waveform and spectrum of a composite encrypted signal after encryption of a narrowband LFM; fig. 4 is a spectrum comparison of the composite encrypted signal after the narrowband LFM is encrypted and the narrowband LFM, and with reference to fig. 3 and fig. 4, it can be seen that the designed composite encrypted signal has a large bandwidth and a high degree of confusion compared with the original LFM signal. Fig. 5 is a time-frequency diagram comparing a composite encrypted signal encrypted by a narrowband LFM with a narrowband LFM, where after the signal is encrypted, general time-frequency analysis cannot check signal characteristics, and the designed encrypted signal has low interception characteristics. Fig. 6 and fig. 7 show that, when the composite encrypted signal encrypted by the narrowband LFM and the pulse pressure obtained when the narrowband LFM detects the point target are compared with the MTD result, the detection performance of the point target is not affected after the encrypted signal is correctly decrypted. Fig. 8 is a comparison diagram of a designed composite encrypted signal with a narrowband LFM encrypted and a wideband LFM signal with a bandwidth equal to that of the composite encrypted signal, and it can be seen that, due to the decryption step, even if the wideband encrypted signal is transmitted, the decrypted signal still becomes a narrowband LFM, so that the resolution is poor and multiple scattering points accumulate. Fig. 9 is a graph comparing pulse pressure results of a conventional decryption method and a decryption method based on local detection according to the present invention, and it can be seen that the proposed decryption method can effectively reduce signal-to-noise ratio loss when dealing with an expansion target.
Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (7)
1. The low interception waveform design method based on the composite encryption is characterized by comprising the following steps of:
a1, a signal source generates an LFM signal as a pre-encryption signal;
a2, taking the pseudo-random two-phase code as an encryption sequence, and multiplying the encryption sequence by the waveform generated in the step A1 to encrypt the encryption sequence so as to form a low-interception waveform;
A3, up-converting the encrypted waveform in the step A2 and using the waveform as a radar transmitting signal.
2. The method for designing a low-interception waveform based on composite encryption according to claim 1, wherein the implementation process of the step A2 specifically comprises the following sub-steps:
a21, generating a pseudo-random sequence c (t), wherein the sequence is subjected to uniform distribution (-1, 1), binarizing the sequence, and representing the binarized pseudo-random sequence in a chip form:
Where c n represents the nth chip of the binarized pseudo-random sequence c B (T), T c represents the duration of each chip, N c represents the number of chips, and g (T) represents a rectangular function;
a22, representing the LFM signal generated by the signal source in the step A1 in a chip form as follows:
Where s n represents the nth chip of the signal s (T), and T c represents the duration of each chip;
A23, multiplying s (t) by c B (t) generated in step a21, to obtain an encrypted waveform d (t), expressed as: d (t) =s (t) c B (t).
3. The low interception waveform processing method based on the composite encryption is characterized by comprising the following steps of:
B1, a transmitting end transmits the radar signal obtained in the step A3;
b2, the receiving end uses an expansion target processing method based on local detection to perform down-conversion and decryption processing on the obtained received echo signals;
and B3, performing pulse compression and MTD processing on the decrypted target echo signals, and extracting the distance and Doppler information of the target.
4. The method for processing low-interception waveform based on composite encryption as claimed in claim 3, wherein the implementation process of step B2 specifically comprises the following sub-steps:
B21, firstly modeling the echo of the expansion target, assuming that M pulses are shared in one coherent processing interval, the slow time intermediate frequency echo model of the mth pulse received by the radar can be expressed as:
Wherein Δt m = (m-1) T, T is pulse repetition time, τ p is a delay of a P-th scattering point of the target relative to the radar, v is a speed of the scattering point, τ p-2v(t+△Tm)/c represents a delay corresponding to the m-th pulse, P represents a total scattering point number of the extended target, and a p,τp represents a scattering coefficient and a corresponding delay of the P-th scattering point, respectively;
b22 down-converting r (t, m) to obtain baseband echo signal r d (t, m), denoted as
Wherein A p′＝Apexp{j2πfcτp is a constant term; f d＝2vfc/c denotes the Doppler frequency of the target;
B23, decrypting the baseband echo signal r d (t, m) in step B22 by using the extended target processing method based on local detection.
5. The method for processing low-interception waveform based on composite encryption as claimed in claim 4, wherein the implementation process of step B23 comprises the steps of:
B231, firstly determining echo delay corresponding to the distance interval of interest, and dividing a local detection window according to a range resolution unit of the narrowband waveform;
B232, then traversing each segment in the domain which is possibly the target echo by using c (t), wherein all echo segments are contained in the local detection window, and zero filling is carried out on each window before decryption so that the length of each window is equal to the length of the local detection window;
B233, assuming the radar is in tracking mode, so the corresponding distance of each window where the target may be is known; therefore, only a few points around the peak after correlation with s (t) are taken and all peaks within the local detection window are added;
and B234, finally, carrying out threshold detection on the summation value to judge whether a target exists in the local detection window.
6. The method for processing low-interception waveform based on complex encryption as claimed in claim 5, wherein the decrypted echo signal can be expressed as:
wherein t p,m＝τp-2v(t+△Tm)/c.
7. The method for processing a low-interception waveform based on complex encryption as claimed in claim 4, wherein τ p＝2Rp/c,Rp is the relative distance between the position of the p-th scattering point of the target and the radar.
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| CN118549892A (en) * | 2024-07-26 | 2024-08-27 | 中国人民解放军国防科技大学 | Method and device for modulating waveform of cryptographic watermark radar, electronic equipment and storage medium |
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| CN118549892A (en) * | 2024-07-26 | 2024-08-27 | 中国人民解放军国防科技大学 | Method and device for modulating waveform of cryptographic watermark radar, electronic equipment and storage medium |
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