CN115390020A - MCPC signal intermittent sampling interference suppression method and device and radar equipment - Google Patents
MCPC signal intermittent sampling interference suppression method and device and radar equipment Download PDFInfo
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Abstract
The method starts from the aspects of waveform design and interference suppression, adopts an MCPC multiphase subcarrier coding structure, adopts a chaotic sequence to code a chip of each subcarrier, and designs and transmits a radar signal waveform to be transmitted by utilizing the mutual shielding concept among the subcarriers; meanwhile, the fractional Fourier transform-based segment correlation processing is combined, firstly, the fractional Fourier transform and the filtering processing are carried out on the received echo signals, interference and real echo signals are sorted, the sampled sub-carriers are identified, the radar signals to be transmitted and the echo signals without the sampled sub-carriers are matched, and the interference removal result is obtained. By adopting the method, the interference of 3 typical ISRJ false targets can be effectively inhibited, and a new solution is provided for the radar anti-interference problem.
Description
Technical Field
The application relates to the technical field of radar signal processing, in particular to an MCPC signal intermittent sampling interference suppression method and device and radar equipment.
Background
With the continuous development of modern electronic countermeasure technology, the signal interference technology for military radars is continuously improved, wherein the intermittent-sampling and Repeater Interference (ISRJ) based on Digital Radio Frequency (DRFM) memory technology is widely applied to radar signal interference. The intermittent sampling forwarding interference is a novel coherent interference derived from a digital radio frequency memory, and can simultaneously have the pressure type and deception type effects by discontinuously sampling radar transmitting signals and then carrying out corresponding modulation and forwarding. Coherent interference signals generated by the ISRJ technology have strong coherence with radar emission signals, so that larger pulse pressure gain can be obtained, and serious threat is formed to the survival capability of the radar. Typical intermittent sample forwarding interference patterns at present are mainly intermittent sample direct Interference (ISDRJ), intermittent sample repeat forwarding Interference (ISRRJ) and intermittent sample cyclic forwarding Interference (ISCRJ).
Although there have been a lot of research results for eliminating the intermittent sampling interference, the existing research results cannot effectively suppress the interference of 3 typical ISRJ decoys at the same time, and there are situations that the interference simulation performance cannot meet the actual requirements.
Disclosure of Invention
In view of the above, it is necessary to provide an MCPC signal intermittent sampling interference suppression method, device and radar apparatus.
An interference suppression method for intermittent sampling of an MCPC signal, the method comprising:
based on an orthogonal frequency division multiplexing technology, a plurality of subcarriers and phase codes corresponding to the subcarriers are constructed, and a multi-carrier phase code radar signal is constructed according to the subcarriers and the phase codes.
And performing time domain coding on the multi-carrier phase coding radar signal according to a pre-generated chaotic sequence, intercepting the code length of each subcarrier with equal interval of the coded signal, and generating a radar signal to be transmitted.
And transmitting the radar signal to be transmitted and receiving an echo signal, wherein the echo signal comprises a real echo signal and intermittent sampling forwarding interference.
And performing fractional Fourier transform on the echo signal, performing frequency domain filtering by adopting a plurality of subcarrier filters, and performing time domain conversion on a filtering result to obtain time domain signals of different frequency parts of the echo signal.
And according to the result of matched filtering of the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal, sorting the real echo signal and the intermittent sampling forwarding interference, and identifying the sampled subcarrier signal.
And performing matched filtering on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
An apparatus for interference suppression of intermittent sampling of an MCPC signal, the apparatus comprising:
the code construction module is used for constructing a plurality of subcarriers and phase codes corresponding to the subcarriers based on an orthogonal frequency division multiplexing technology, and constructing a multi-carrier phase code radar signal according to the subcarriers and the phase codes;
and the coding module is used for carrying out time domain coding on the multi-carrier phase coding radar signal according to the pre-generated chaotic sequence, intercepting the code length of the equal interval in each subcarrier of the coded signal and generating the radar signal to be transmitted.
And the transmitting module is used for transmitting the radar signal to be transmitted and receiving an echo signal, wherein the echo signal comprises a real echo signal and intermittent sampling forwarding interference.
The anti-intermittent forwarding interference module is used for performing fractional Fourier transform on the echo signal, then performing frequency domain filtering by adopting a plurality of subcarrier filters, and performing time domain conversion on a filtering result to obtain time domain signals of different frequency parts of the echo signal; according to the result of matched filtering of the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal, sorting the real echo signal and the intermittent sampling forwarding interference, and identifying a sampled subcarrier signal; and performing matched filtering on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
A radar apparatus comprising a memory, a processor and a transceiver module, the memory storing a computer program, the processor implementing the method of any one of the above when executing the computer program.
According to the interference suppression method, device and radar equipment for MCPC signal intermittent sampling, an SCC-MCPC waveform is designed from the aspects of waveform design and interference suppression. The multi-phase subcarrier coding structure of the MCPC is adopted, the chaotic sequence is adopted to carry out time domain phase coding on the chips of each subcarrier, and the idea of mutual shielding among the subcarriers is utilized to carry out differential processing on signals in different subcarrier channels, so that all signal subcarrier information cannot be completely sampled by intermittent sampling, and the signals have good property of resisting intermittent sampling interference; the method comprises the steps of performing fractional Fourier transform on received echo signals, performing filtering processing, sorting intermittent sampling forwarding interference and real echo signals, identifying sampled subcarriers, performing matching processing on radar signals to be transmitted and echo signals without the sampled subcarrier signals, and obtaining interference removal results. By adopting the method, the interference of 3 typical ISRJ false targets can be effectively inhibited, and a new solution is provided for the radar anti-interference problem.
Drawings
FIG. 1 is a diagram illustrating an exemplary application scenario of the interference suppression method for MCPC signal intermittent sampling;
FIG. 2 is a schematic flow chart illustrating an embodiment of an interference suppression method for intermittent sampling of MCPC signals;
FIG. 3 is a diagram of a fractional Fourier transform in one embodiment;
FIG. 4 is a graph comparing FFT and FrFT transforms of an SCC-MCPC signal in another embodiment, wherein (a) is the FFT transform of the SCC-MCPC signal and (b) is the FrFT transform of the SCC-MCPC signal;
FIG. 5 is a diagram of a SCC-MCPC signal model in another embodiment;
FIG. 6 is a graph of the fuzzy function of the SCC-MCPC signal and the LFM signal under the same bandwidth, wherein (a) is the fuzzy function of the SCC-MCPC signal and (b) is the fuzzy function of the LFM signal;
FIG. 7 is a signal model diagram of an alternate embodiment of an intermittently sampled direct-to-repeat interference;
FIG. 8 is a signal model diagram of an intermittent sample repeat-and-forward interference in another embodiment;
FIG. 9 is a signal model diagram of an intermittent sampling cycle-forward interference in another embodiment;
fig. 10 is a diagram illustrating suppression effects of different intermittent sampling forwarding interferences in another embodiment, where (a) is before the suppression of the intermittent sampling direct forwarding interference, (b) is after the suppression of the intermittent sampling direct forwarding interference, (c) is before the suppression of the intermittent sampling repeat forwarding interference, (d) is after the suppression of the intermittent sampling repeat forwarding interference, (e) is before the suppression of the intermittent sampling cyclic forwarding interference, and (f) is after the suppression of the intermittent sampling cyclic forwarding interference;
fig. 11 is a SJR improvement factor for different SNRs and SJRs conditions in another embodiment, where (a) is SJR = -6dB for matched filters, (b) is SJR = -9dB for matched filters, (c) is SJR = -12dB for matched filters, and (d) is SJR = -15dB for matched filters;
fig. 12 is a graph comparing simulation results of improvement factors of signal SJR of CC-MCPC and SCC-MCPC under different SNRs and SJRs in another embodiment, wherein (a) is SJR = -6dB, (b) is SJR = -9dB, (c) is SJR = -12dB, and (d) is SJR = -15dB;
FIG. 13 is a flow chart of a segmented pulse compression immunity signal in another embodiment;
FIG. 14 is a block diagram of an embodiment of an interference suppression apparatus for intermittent sampling of MCPC signals;
fig. 15 is an internal structural diagram of a radar apparatus in one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The working principle of the intermittent sampling and forwarding Interference (ISRJ) is that after an interferer based on Digital Radio Frequency Memory (DRFM) intercepts and stores a certain segment of a radar transmission signal, the segment is forwarded once or many times, and the process of interception-storage-forwarding is repeated until the pulse ends.
The method for suppressing the interference of the intermittent sampling of the MCPC signal can be applied to the application environment shown in FIG. 1. The radar device 102 may emit an electric wave, and after the electric wave reaches the scatterer target 104, the electric wave reflects a return electric wave, and the radar device 102 receives the return electric wave to locate the scatterer target 104, and when there is intermittent sampling interference, the jammer 106 intermittently samples the electric wave, so as to form a coherent jammer string that interferes with the radar device 102 to locate the scatterer target.
In one embodiment, as shown in fig. 2, there is provided an MCPC signal intermittent sampling interference suppression method, including the steps of:
step 200: based on the orthogonal frequency division multiplexing technology, a plurality of subcarriers and phase codes corresponding to the subcarriers are constructed, and the multi-carrier phase code radar signal is constructed according to the subcarriers and the phase codes.
Orthogonal Frequency Division Multiplexing (OFDM) technology is one of multicarrier modulation technologies, realizes parallel transmission of high-speed serial data through Frequency Division Multiplexing, has good multipath fading resistance, and can support multi-user access. The subcarrier is a concept in the OFDM technology, and one OFDM signal is composed of a plurality of subcarriers, and for each subcarrier, phase coding of multiple bits is set. In order to meet the requirement of orthogonal sub-carrier frequencies in the OFDM technology, the width of each chip in phase coding is equal, and the interval between adjacent sub-carrier frequencies is the reciprocal of the chip width.
The multi-carrier phase coding radar signal (MCPC-OFDM signal) has an ideal fuzzy function, high target resolution characteristics and good detection capability, and the MCPC-OFDM signal combines multi-carrier chaotic phase coding and orthogonal frequency division multiplexing signals, so that the MCPC-OFDM signal has excellent fuzzy function performance, pulse pressure performance and low interception performance. The method has the advantages of good anti-attenuation capability, large time-bandwidth product and high frequency spectrum utilization rate of the OFDM signal, and also has the advantages of orthogonality of the chaotic sequence, capability of generating a large amount and different lengths.
The multi-carrier phase coding radar signal constructed in the step can be subjected to flexible waveform design, so that coding can be performed on a time domain and a frequency domain.
Step 202: and carrying out time domain coding on the multi-carrier phase coding radar signal according to the pre-generated chaotic sequence, intercepting the length of the code piece with the equal interval in each subcarrier of the coded signal, and generating the radar signal to be transmitted.
A chaotic time series is a type of motion that determines irregularities in the system. The time domain refers to the variation of the multi-carrier phase-coded radar signal with time, and the frequency domain is a coordinate system used for describing the characteristics of the signal in terms of frequency.
In the step, the time domain coding is carried out on the multi-carrier phase coding radar signal on the frequency domain through the chaotic sequence, and decorrelation is carried out between pulses and in the pulses of the multi-carrier phase coding radar signal, so that pseudo-random to a certain degree is formed, the video characteristics of the whole pulse cannot be sampled when intermittent sampling interference is carried out, the decorrelation between an echo signal and an intermittent sampling signal is increased, and the interference on the intermittent sampling is improved.
In the invention, the radar signal to be transmitted is named as: subcarrier masking-multicarrier chaotic orthogonal frequency division multiplexing signals, which are all called in english: the SubCrrier Cover Multiple Carrier Orthogonal Frequency, referred to as SCC-MCPC signal.
The radar signal to be transmitted is obtained by respectively intercepting fixed lengths of each section of subcarrier from the perspective of a signal structure by introducing the idea of mutually shielding subcarriers on the basis of an MCPC signal, and because the discontinuous property of interference sampling is intermittently adopted, all subcarrier signals can not be completely sampled, and different subcarriers are in a mutual orthogonal relation, so that no matter how the sampling is carried out in a time domain, the sampled signal section can be removed by utilizing the orthogonality among the subcarriers, and the signal can effectively inhibit ISRJ interference.
Step 204: and transmitting a radar signal to be transmitted and receiving an echo signal, wherein the echo signal comprises a real echo signal and intermittent sampling forwarding interference.
The radar equipment transmits a radar signal to be transmitted, after the radar signal to be transmitted reaches a scatterer target, a return electric wave (namely a real echo signal) is reflected, under the condition that intermittent sampling forwarding interference exists, the echo signal received by the radar equipment also comprises the intermittent sampling forwarding interference,
the echo signals received by the radar device may be described as:
s Echo (t)＝s R (t)+s ISRJ (t)+n(t) (1)
wherein s is Echo (t) is the echo signal, s R (t) is the true echo signal of the scattering target at distance R, s ISRJ (t) is ISRJ interference and n (t) is ambient noise.
Step 206: and after the fractional Fourier transform is carried out on the echo signals, frequency domain filtering is carried out by adopting a plurality of subcarrier filters, and time domain conversion is carried out on the filtering results to obtain time domain signals of different frequency parts of the echo signals.
Fractional Fourier Transform (FrFT) is based on Fourier Transform, a rotation factor alpha is introduced, the relation between a signal time domain and a signal frequency domain is established through different alpha, and the basic idea is to utilize the Fractional Fourier Transform to carry out rotation separation on the signal, so that the purpose of suppressing noise is achieved. The separated signals are restored to original signals through reverse rotation of the time frequency plane. The p-order Fourier transform can be regarded as a time domain frequency domain image formed by rotating the coordinate axis of the signal on the time domain frequency domain by an angle of alpha = p pi/2 anticlockwise around the origin and observing the signal through different angles. And when the rotation angle is pi/2, the Fourier transform is carried out. As shown in fig. 3.
The p-order FrFT expression of the radar signal s (t) to be transmitted is as follows:
kernel function K p The expression of (t, u) is:
wherein,
α = p π/2, τ being the time delay and n being an integer.
The radar signal to be transmitted (i.e. the SCC-MCPC signal) has a sudden phase change at the signal symbol boundary, which causes discontinuity (aliasing) of the signal spectrum, and the resulting spectral leakage interferes with the FFT filtering. Aiming at the problem, frFT filtering is introduced, so that the influence of frequency spectrum leakage of signals can be reduced, the coupling between subcarrier signals is reduced, subcarriers are easier to separate in a frequency domain, and the filtering efficiency is higher. Fig. 4 is a graph comparing the FFT transformation and the FrFT transformation of the signal, wherein (a) is the FFT transformation of the SCC-MCPC signal, and (b) is the FrFT transformation of the SCC-MCPC signal. As can be seen from fig. 4, compared with the original FFT transform, the coupling between subcarriers in the frequency domain is high, the energy aggregation is strong, the filtering effect is poor, the signal coupling in the u domain after FrFT transform is lower, the energy aggregation is reduced, and the filtering separation of subcarriers is facilitated.
Step 208: and according to the result of matched filtering of the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal, sorting the real echo signal and the intermittent sampling forwarding interference, and identifying the sampled subcarrier signal.
The signal of the real echo signal after frequency domain filtering and time domain conversion by the subcarrier filter has autocorrelation with the original transmitting signal, so the result peak values of the correlation operation are all close; in the intermittent sampling forwarding interference signal, only the result of the correlation operation between the sampled subcarrier signal and the original transmitting signal has a peak value, and the rest has no peak value.
Step 210: and performing matched filtering on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
In the method for suppressing the interference of the intermittent sampling of the MCPC signal, an SCC-MCPC waveform is designed from the viewpoint of waveform design and interference suppression. The MCPC multi-phase subcarrier coding structure is adopted, the chaos sequence is adopted to carry out time domain phase coding on the chip of each subcarrier, and the idea of mutual shielding among the subcarriers is utilized to carry out distinguishing processing on signals in different subcarrier channels, so that all signal subcarrier information cannot be completely sampled by intermittent sampling, and the signals have good property of resisting intermittent sampling interference; the method comprises the steps of performing fractional Fourier transform on received echo signals, performing filtering processing, sorting intermittent sampling forwarding interference and real echo signals, identifying sampled subcarriers, performing matching processing on radar signals to be transmitted and echo signals without the sampled subcarrier signals, and obtaining interference removal results. By adopting the method, the interference of 3 typical ISRJ false targets can be effectively inhibited, and a new solution is provided for the radar anti-interference problem.
In one embodiment, the envelope expression of the radar signal to be transmitted in step 202 is:
where P is the number of subcarriers, M is the number of codes encoded by the subcarriers, μ (t) is the complex envelope of each subcarrier,
the amplitude-phase weighting coefficient for the nth subcarrier,
for the chaotic phase encoded value at mth chip on nth subcarrier, f n = (n-1) Δ f is carrier frequency of nth subcarrier, wherein
For subcarrier frequency spacing, t B Duration of a single chip, t B And = M/P is the average segment length of the number of subcarriers taken by the number of M phase codes.
Preferably, the iterative expression of logstic chaotic code is
Chaotic attraction domain is x k ∈[-1,1]. By selecting the process variable x k That is, the corresponding chaotic sequence can be generated according to the mapping expression. The generated chaos sequence needs quantization coding, and the quantization rule is shown as formula (6).
a n ＝2π·ceil(N P x p +0.5)/N P (6)
According to the quantization rule, by pair N P Two-phase coding and different multi-phase coding can be obtained. Here, N is selected P =2 denotes chaotic bi-phase coding. Let { a 1 ,a 2 ,a 3 ,...,a M×N Is the final two-phase coded sequence after binary quantization, where E k For original mix sequence { x 1 ,x 2 ,x 3 ,...,x M×N The mean of, its expression is:
obtaining a chaotic phase encoding value on the mth chip on the nth subcarrier as follows:
the time-frequency structure of the SCC-MCPC signal is shown in FIG. 5. In fig. 5, the dotted line part is the original MCPC-OFDM signal, and the shaded part is the time-frequency diagram of the SCC-MCPC signal.
Compared with the OFDM signal, the SCC-MCPC signal adds one-dimensional modulation, so that the modulation mode of the signal is more flexible (phase). The SCC-MCPC signal is obtained by intercepting a part (shaded part) of the MCPC signal at equal intervals in each segment of subcarriers, on the basis of which, due to the discontinuous nature of intermittently adopting interference sampling, all subcarrier signals cannot be completely sampled, and different subcarriers are in a mutually orthogonal relationship, so that no matter how the sampling is carried out in the time domain, the signal segment sampled in the radar transmission signal can be removed by utilizing the orthogonality between the subcarriers.
In order to analyze the anti-interference effect of the SCC-MCPC signal, a fuzzy function calculation formula can be obtained by combining the SCC-MCPC signal envelope expression (4) as follows.
Where χ (τ, v) is the blurring function of s (t).
Taking the SCC-MCPC signal of 8 carriers as an example, the ambiguity function of a Linear Frequency Modulation (LFM) signal under the same bandwidth is shown in fig. 6, where (a) is an ambiguity function diagram of the SCC-MCPC signal and (b) is an ambiguity function diagram of the LFM signal.
As can be seen from FIG. 6, the energy of the LFM signal fuzzy function is more concentrated at the origin, the pattern is similar to the shape of a beveled edge, and the distance Doppler coupling will cause the distance measurement to be inaccurate. The SCC-MCPC signal modulated by the chaotic phase code has an ideal fuzzy function, a Doppler distance Doppler plane of the fuzzy function is flat, amplitude fluctuation is small, a single sharp peak value is arranged at an origin, side lobes outside the origin are distributed uniformly and flat, and the whole signal is close to a picture pin shape. Compared with LFM signals, the method has higher measurement precision and excellent target resolution capability.
In one embodiment, the expression of the real echo signal in step 204 is:
in the formula,
is echo time delay, A is echo signal amplitude, c is propagation speed of light in air, envelope of radar signal to be transmitted, P is number of subcarriers, M is number of coded subcarriers, μ (t) is complex envelope of each subcarrier,
the magnitude-phase weighting coefficient for the nth subcarrier,
for the chaotic phase encoded value at mth chip on nth subcarrier, f n = (n-1) Δ f is carrier frequency of nth subcarrier, wherein
Is a subcarrier frequency interval, t B Duration of a single chip, t B And the = M/P is the average segment length of M phase code numbers by the number of subcarriers.
In one embodiment, the intermittently sampled retransmission interference in step 204 comprises: intermittent sampling direct forwarding interference, intermittent sampling repeat forwarding interference, and/or intermittent sampling cyclic forwarding interference.
The time domain expression of the intermittent sampling direct forwarding interference is as follows:
wherein H is the number of slices, T J For slice width, s (t)A signal is transmitted for the intercepted radar. A signal model diagram of the intermittent sampling direct-to-forward interference is shown in fig. 7.
The time domain expression of the intermittent sampling repeat forwarding interference is as follows:
wherein, N is the forwarding number of each slice, and α (h, N) = (h-1) (N + 1) + N is the delay coefficient corresponding to the nth forwarding of the h slice. A signal model diagram of intermittent sampling repetitive retransmission interference is shown in fig. 8.
The time domain expression of the intermittent sampling cyclic forwarding interference is as follows:
wherein α (h) = h (h + 1)/2-1 is a delay coefficient β (h, n) = n (n + 1)/2 + h (n-1) corresponding to the h-th slice, and the delay coefficient corresponding to the n-th forwarding of the h-th slice is obtained. A signal model diagram of the intermittent sampling loop retransmission interference is shown in fig. 9.
In one embodiment, step 208 includes: performing correlation operation on time domain signals of different frequency parts of the radar signal to be transmitted and the echo signal to obtain a correlation operation result; when the peak values in the correlation operation result are all close, the real echo signal is obtained; when the frequency band without the peak value exists in the correlation operation result, the interference is forwarded for intermittent sampling; and determining the sampled subcarrier signal according to the correlation operation result corresponding to the intermittent sampling forwarding interference.
In one embodiment, step 210 includes: and performing correlation operation on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
In one embodiment of simulation analysis, the suppression effect on different intermittent sampling forwarding interferences is shown in fig. 10, where (a) is before the intermittent sampling direct forwarding interference suppression, (b) is after the intermittent sampling direct forwarding interference suppression, (c) is before the intermittent sampling repeat forwarding interference suppression, (d) is after the intermittent sampling repeat forwarding interference suppression, (e) is before the intermittent sampling cycle forwarding interference suppression, and (f) is after the intermittent sampling cycle forwarding interference suppression.
In one embodiment, step 210 is followed by: calculating the signal-to-interference ratio of the real echo signal and the intermittent sampling forwarding interference according to the real echo signal and the intermittent sampling forwarding interference; carrying out short-time Fourier transform on the echo signal to obtain a short-time Fourier transform result; filtering the short-time Fourier transform result by adopting a normalized filter; obtaining pulse compression output after discontinuous sampling interference suppression according to the short-time Fourier transform result and the normalized filtering result; calculating the signal-to-interference ratio of pulse compression output after intermittent sampling interference suppression; and evaluating the performance of the MCPC signal intermittent sampling interference suppression method according to the difference value of the signal-to-interference ratio of the real echo signal and the intermittent sampling forwarding interference and the signal-to-interference ratio of the pulse compression output after the intermittent sampling interference suppression.
Specifically, the received echo signal may be obtained by Short-Time Fourier Transform (STFT) Transform:
the normalized filter H (f) can be expressed as:
H(f)＝|S m (t,f)| 2 (15)
the pulse pressure output after interrupting the sampling interference suppression is:
P(f)＝H(f)×∫S m (t)exp(-j2πft)dt (16)
the invention adopts SJR improvement factors to evaluate the interference suppression performance. It can be expressed as:
δ SJR ＝SJR PC -SJR (17)
in the formula, SJR PC Is the SJR value after pulse compression.
In a specific embodiment, the rejection performance of the SCC-MCPC signal is evaluated, and the anti-interference effect of the SCC-MCPC signal is shown in fig. 11 for different signal-to-noise ratios (SNRs), where (a) is SJR = -6dB for the matched filter, (b) is SJR = -9dB for the matched filter, (c) is SJR = -12dB for the matched filter, and (d) is SJR = -15dB for the matched filter. Simulation parameters of the input SCC-MCPC signal are as follows: the carrier frequency is 35GHZ, the signal bandwidth is 32MHZ, the pulse repetition period is 1280us, the sampling rate is 64MHZ, and the pulse width is 128us. As can be seen from fig. 11, under the same parameter criteria, the SCC-MCPC signal anti-interference method provided by the present invention has SJR improvement factors 6 to 12dB higher than those of the conventional MCPC signal under different SJRs and SNRs compared to the conventional MCPC signal.
The Peak-to-Average power Ratio (PAPR) expression of the signal is: '
Wherein, the peak value MAX (| X) 2 (t) |) is the peak power E (X) of the signal 2 (t)) is the average power of the signal. Under the parameters set by the invention, the PAPR of the MCPC signal is 9.0309, and the PAPR of the SCC-MCPC signal is 9.6433e-16. The constant modulus characteristic of the signal of the invention is better than that of the traditional MCPC.
In a comparative experiment, the CC _ MCPC signal and the radar signal to be transmitted (i.e., the SCC-MCPC signal) proposed in the present invention are subjected to a comparative experiment, so as to have a good anti-ISRJ signal, this embodiment analyzes the interference suppression effect of the waveform signals of the two signals under different SNRs and SJRs, and a simulation result pair of improvement factors of the CC-MCPC and the SCC-MCPC signal SJR is shown in fig. 12, where (a) is SJR = -6dB, (b) is SJR = -9dB, (c) is SJR = -12dB, and (d) is SJR = -15dB.
As can be seen from FIG. 12, under the same parameter standard, the SCC-MCPC signal anti-interference method has a better effect of resisting intermittent sampling interference compared with the SCC-MCPC under different SJRs and SNRs. The SCC-MCPC signal anti-interference suppression method is 5-12dB higher than the SJR improvement factor of the CC-MCPC signal.
In one embodiment, the interference rejection flow of fractional fourier filter filtering subcarrier pulse compression is shown in fig. 13. The specific implementation process is as follows:
(1) After fractional Fourier transform is carried out on a radar receiving signal, frequency domain filtering is carried out through a corresponding subcarrier filter, and the radar receiving signal is converted into a time domain signal after the frequency domain filtering, so that time domain signals of different frequency parts of the receiving signal are obtained;
(2) Respectively carrying out matched filtering on the original transmitting signal and the filtering results of different subcarrier filters;
(3) If the result is a false target, the result of the correlation operation between the sampled subcarrier signal and the original transmitting signal has a peak value, and the rest has no peak value.
(4) And performing matched filtering by using the original transmitting signal and the echo signal without the sampled segment to obtain an interference removing result.
It should be understood that, although the steps in the flowchart of fig. 1 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 1 may include multiple sub-steps or multiple stages that are not necessarily performed at the same time, but may be performed at different times, and the order of performing the sub-steps or stages is not necessarily sequential, but may be performed alternately or alternately with other steps or at least some of the sub-steps or stages of other steps.
In one embodiment, as shown in fig. 14, there is provided an MCPC signal intermittent sampling interference suppression apparatus, including: the code constructing module, the coding module, the transmitting module and the intermittent forwarding interference resisting module are arranged, wherein:
the code construction module is used for constructing a plurality of subcarriers and phase codes corresponding to the subcarriers based on an orthogonal frequency division multiplexing technology, and constructing a multi-carrier phase code radar signal according to the subcarriers and the phase codes;
and the coding module is used for carrying out time domain coding on the multi-carrier phase coding radar signal according to the pre-generated chaotic sequence, intercepting the code length of the equal interval in each subcarrier of the coded signal and generating the radar signal to be transmitted.
And the transmitting module is used for transmitting the radar signal to be transmitted and receiving the echo signal, wherein the echo signal comprises a real echo signal and intermittent sampling forwarding interference.
The anti-intermittent forwarding interference module is used for performing fractional Fourier transform on the echo signal, then performing frequency domain filtering by adopting a plurality of subcarrier filters, and performing time domain conversion on a filtering result to obtain time domain signals of different frequency parts of the echo signal; according to the result of matched filtering of the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal, sorting the real echo signal and the intermittent sampling forwarding interference, and identifying the sampled subcarrier signal; and performing matched filtering on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
In one embodiment, the expression of the envelope of the radar signal to be transmitted in the coding module is shown as formula (4).
In one embodiment, the expression of the real echo signal in the transmitting module is shown as equation (10).
In one embodiment, the intermittent sample forwarding interference in the transmitting module comprises: intermittent sampling direct forwarding interference, intermittent sampling repeat forwarding interference, and/or intermittent sampling cyclic forwarding interference.
The time domain expression of the intermittent sampling direct forwarding interference is shown as formula (11).
The time domain expression of the intermittent sampling repeat forwarding interference is shown in formula (12).
The time domain expression of the intermittent sampling cyclic forwarding interference is shown in formula (13).
In one embodiment, the anti-intermittent forwarding interference module is further configured to perform correlation operation on time domain signals of different frequency portions of the radar signal to be transmitted and the echo signal to obtain a correlation operation result; when the peak values in the correlation operation result are all close, the real echo signal is obtained; when the frequency band without the peak value exists in the correlation operation result, the interference is forwarded for intermittent sampling; and determining the sampled subcarrier signal according to the correlation operation result corresponding to the intermittent sampling forwarding interference.
In one embodiment, the anti-intermittent forwarding interference module is further configured to perform correlation operation on the radar signal to be transmitted and the echo signal from which the sampled subcarrier signal is removed, so as to obtain an interference removal result.
In one embodiment, the anti-interference module further comprises an anti-interference evaluation module, which is used for calculating the signal-to-interference ratio of the real echo signal and the intermittent sampling forwarding interference according to the real echo signal and the intermittent sampling forwarding interference; carrying out short-time Fourier transform on the echo signal to obtain a short-time Fourier transform result; filtering the short-time Fourier transform result by adopting a normalized filter; according to the short-time Fourier transform result and the normalized filtering result, obtaining pulse compression output after discontinuous sampling interference suppression; calculating the signal-to-interference ratio of pulse compression output after the intermittent sampling interference suppression; and evaluating the performance of the MCPC signal intermittent sampling interference suppression method according to the difference value of the signal-to-interference ratio of the real echo signal and the intermittent sampling forwarding interference and the signal-to-interference ratio of the pulse compression output after the intermittent sampling interference suppression.
For specific limitations of the MCPC signal intermittent sampling interference suppression apparatus, reference may be made to the above limitations of the MCPC signal intermittent sampling interference suppression method, which is not described herein again. The modules in the above mentioned MCPC signal intermittent sampling interference suppression device can be wholly or partially implemented by software, hardware and their combination. The modules can be embedded in a hardware form or independent of a processor in the radar device, and can also be stored in a memory in the radar device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a radar apparatus is provided, which may be a terminal, and an internal structure thereof may be as shown in fig. 15. The radar apparatus includes a processor, a memory, a network interface, a display screen, and an input device connected through a system bus. Wherein the processor of the radar apparatus is configured to provide computational and control capabilities. The memory of the radar device includes a nonvolatile storage medium, an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operating system and the computer program to run on the non-volatile storage medium. The network interface of the radar device is used for communicating with an external terminal through network connection. The computer program is executed by a processor to implement an interference suppression method for intermittent sampling of MCPC signals. The display screen of the radar equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the radar equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on a shell of the radar equipment, an external keyboard, a touch pad or a mouse and the like.
It will be appreciated by those skilled in the art that the structure shown in fig. 15 is a block diagram of only a portion of the structure associated with the present application, and does not constitute a limitation on the radar apparatus to which the present application is applied, and that a particular radar apparatus may include more or fewer components than shown in the figures, or combine certain components, or have a different arrangement of components.
In an embodiment, a radar apparatus is provided, comprising a memory storing a computer program and a processor implementing the steps of the method in the above-described method embodiments when the processor executes the computer program.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.
Claims (10)
1. An interference suppression method for intermittent sampling of an MCPC signal, the method comprising:
constructing a plurality of subcarriers and phase codes corresponding to the subcarriers based on an orthogonal frequency division multiplexing technology, and constructing a multi-carrier phase code radar signal according to the subcarriers and the phase codes;
performing time domain coding on the multi-carrier phase coding radar signal according to a pre-generated chaotic sequence, intercepting the length of a chip at an equal interval in each subcarrier of the coded signal, and generating a radar signal to be transmitted;
transmitting the radar signal to be transmitted and receiving an echo signal, wherein the echo signal comprises a real echo signal and intermittent sampling forwarding interference;
performing fractional Fourier transform on the echo signal, performing frequency domain filtering by adopting a plurality of subcarrier filters, and performing time domain conversion on a filtering result to obtain time domain signals of different frequency parts of the echo signal;
according to the result of matched filtering of the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal, sorting the real echo signal and the intermittent sampling forwarding interference, and identifying a sampled subcarrier signal;
and performing matched filtering on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
2. The method according to claim 1, wherein the multi-carrier phase-coded radar signal is time-domain coded according to a pre-generated chaotic sequence, and the coded signal is intercepted for each sub-carrier with a chip length of a middle interval to generate a radar signal to be transmitted, and in the step, an envelope expression of the radar signal to be transmitted is as follows:
where P is the number of subcarriers, M is the number of codes encoded by the subcarriers, μ (t) is the complex envelope of each subcarrier,
the magnitude-phase weighting coefficient for the nth subcarrier,
for the chaotic phase encoded value at the m-th chip on the n-th subcarrier, f n = (n-1) Δ f is carrier frequency of nth subcarrier, wherein
For subcarrier frequency spacing, t B Duration of a single chip, t B And = M/P is the average segment length of the number of subcarriers taken by the number of M phase codes.
3. The method according to claim 1, wherein the radar signal to be transmitted is transmitted and an echo signal is received, and the expression of the true echo signal in the step is:
in the formula,
is an echoThe time delay, A is the amplitude of the echo signal, c is the propagation speed of light in the air, the envelope of the radar signal to be transmitted, P is the number of subcarriers, M is the number of codes coded by the subcarriers, mu (t) is the complex envelope of each subcarrier,
the amplitude-phase weighting coefficient for the nth subcarrier,
for the chaotic phase encoded value at the m-th chip on the n-th subcarrier, f n = (n-1) Δ f is carrier frequency of nth subcarrier, wherein
For subcarrier frequency spacing, t B Duration of a single chip, t B And = M/P is the average segment length of the number of subcarriers taken by the number of M phase codes.
4. The method of claim 1, wherein transmitting the radar signal to be transmitted and receiving an echo signal, wherein the intermittently sampling retransmission interference comprises: intermittent sampling direct forwarding interference, intermittent sampling repeated forwarding interference and/or intermittent sampling cyclic forwarding interference;
the time domain expression of the intermittent sampling direct forwarding interference is as follows:
wherein H is the number of slices, T J S (t) is the intercepted radar transmission signal;
the time domain expression of the intermittent sampling repeated forwarding interference is as follows:
wherein, N is the forwarding times of each slice, and alpha (h, N) = (h-1) (N + 1) + N is the h slice for the h slice to go to the th n The corresponding time delay coefficient is forwarded for the second time;
the time domain expression of the intermittent sampling cyclic forwarding interference is as follows:
wherein α (h) = h (h + 1)/2-1 is a delay coefficient β (h, n) = n (n + 1)/2 + h (n-1) corresponding to the nth slice for the nth forwarding.
5. The method of claim 1, wherein the sorting the real echo signal and the intermittent sampling forwarding interference according to the result of performing matched filtering on the time domain signals of different frequency parts of the radar signal to be transmitted and the echo signal, and identifying a sampled subcarrier signal comprises:
performing correlation operation on the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal to obtain a correlation operation result;
when the peak values in the correlation operation result are all similar, the echo signals are real echo signals;
when the frequency band without the peak value exists in the correlation operation result, the interference is transmitted for intermittent sampling;
and determining the sampled subcarrier signal according to the correlation operation result corresponding to the intermittent sampling forwarding interference.
6. The method of claim 1, wherein performing matched filtering on the radar signal to be transmitted and the echo signal from which the sampled subcarrier signal is removed to obtain an interference removal result comprises:
and carrying out correlation operation on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
7. The method according to claim 1, wherein the radar signal to be transmitted and the echo signal from which the sampled subcarrier signal is removed are matched filtered to obtain an interference removal result, and the method further comprises:
calculating the signal-to-interference ratio of the real echo signal and the intermittent sampling forwarding interference according to the real echo signal and the intermittent sampling forwarding interference;
carrying out short-time Fourier transform on the echo signal to obtain a short-time Fourier transform result;
filtering the short-time Fourier transform result by adopting a normalized filter;
obtaining pulse compression output after discontinuous sampling interference suppression according to the short-time Fourier transform result and the normalized filtering result;
calculating the signal-to-interference ratio of pulse compression output after the intermittent sampling interference suppression;
and evaluating the performance of the MCPC signal intermittent sampling interference suppression method according to the difference value between the signal-to-interference ratio of the real echo signal and the intermittent sampling forwarding interference and the signal-to-interference ratio of the pulse compression output after the intermittent sampling interference suppression.
8. An apparatus for interference suppression of intermittent sampling of an MCPC signal, the apparatus comprising:
the code construction module is used for constructing a plurality of subcarriers and phase codes corresponding to the subcarriers based on an orthogonal frequency division multiplexing technology, and constructing a multi-carrier phase code radar signal according to the subcarriers and the phase codes;
the encoding module is used for carrying out time domain encoding on the multi-carrier phase encoding radar signal according to a pre-generated chaotic sequence, intercepting the length of a chip at an equal interval in each subcarrier of the encoded signal and generating a radar signal to be transmitted;
the transmitting module is used for transmitting the radar signal to be transmitted and receiving an echo signal, wherein the echo signal comprises a real echo signal and intermittent sampling forwarding interference;
the anti-intermittent forwarding interference module is used for performing fractional Fourier transform on the echo signal, then performing frequency domain filtering by adopting a plurality of subcarrier filters, and performing time domain conversion on a filtering result to obtain time domain signals of different frequency parts of the echo signal; according to the result of matched filtering of the radar signal to be transmitted and the time domain signals of different frequency parts of the echo signal, sorting the real echo signal and the intermittent sampling forwarding interference, and identifying a sampled subcarrier signal; and performing matched filtering on the radar signal to be transmitted and the echo signal without the sampled subcarrier signal to obtain an interference removal result.
9. The apparatus of claim 8, wherein the envelope of the radar signal to be transmitted in the encoding module is expressed as:
where P is the number of subcarriers, M is the number of codes encoded by the subcarriers, μ (t) is the complex envelope of each subcarrier,
the amplitude-phase weighting coefficient for the nth subcarrier,
for the chaotic phase encoded value at the m-th chip on the n-th subcarrier, f n = (n-1) Δ f is carrier frequency of nth subcarrier, wherein
For subcarrier frequency spacing, t B Duration of a single chip, t B And the = M/P is the average segment length of M phase code numbers by the number of subcarriers.
10. A radar apparatus comprising a memory, a processor and a transceiver module, the memory storing a computer program, characterized in that the processor realizes the steps of the method of any one of claims 1 to 7 when executing the computer program.
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