A method and device for dense target detection based on low intercept waveform

Abstract

The present invention provides a dense target detection device based on a low intercept waveform, comprising: a transmitting end, used to generate a low intercept wave signal, add a cyclic prefix to the low intercept wave signal, obtain a low intercept waveform with a guard interval inserted to prevent cross-distance interference; the low intercept waveform with a guard interval inserted to prevent cross-distance interference is transmitted to a monitoring area as a detection signal after radio frequency modulation; a receiving end, used to receive a detection echo signal reflected from a dense target in the monitoring area, remove the cyclic prefix from the detection echo signal, eliminate the cross-distance interference between distance pixel units, and obtain multiple independent echo signals without crosstalk between distance resolution units; perform FFT processing on the multiple independent echo signals and demodulate them, and then perform IFFT processing to obtain a distance reconstruction signal for the dense target. The present invention uses a method of adding a cyclic prefix to the low intercept wave signal to achieve low interception and range sidelobe suppression for active detection of dense targets.

Description

Technical Field

[0001] The present application relates to the field of sonar detection technology, and in particular to a method and device for dense target detection based on low intercept waveform. Background Art

[0002] With the increasing threats of stealth aircraft and quiet underwater vehicles, how to effectively hide oneself while detecting hostile targets is related to the stealth performance and combat capability of the platform. Low Probability of Interception (LPI) technology is of great significance. Low interception technology was proposed in anti-interference radar. In 1983, JRForest published "Low Probability of Interception Radar Technology" and proposed the low interception probability equation. Since the early 1990s, some developed countries in the West have applied low interception technology to the field of sonar, and have made certain breakthroughs in low interception signal research and receiving system modeling. Due to the particularity of the underwater acoustic channel, the research on low interception technology in sonar has just started in China.

[0003] Traditional radar or sonar achieves active detection by emitting linear frequency modulation (LFM) signals. However, due to the single form of LFM signals, their concealment and security are poor, and they are easily affected by noise and interference signals. Matched filtering will bring about the influence of signal ambiguity function sidelobes, which seriously reduces the target detection performance.

[0004] In 2000, Professor N.Levanon from Israel first introduced the Orthogonal Frequency Division Multiplexing (OFDM) waveform into radar signal processing and conducted in-depth research. MA Sebt and Y. Norouzi et al. used the least squares method to optimize the frequency domain weighting coefficients of the OFDM waveform subcarriers and achieved the suppression of the fuzzy function sidelobe. The research on adaptive OFDM waveform has also been applied to radar imaging, achieving low interception and range sidelobe suppression, and has achieved certain research results.

[0005] For densely packed multiple targets, it is necessary to suppress interference and range sidelobes between targets. Suppressing range sidelobes can be achieved by improving the transmit waveform. With the support of the US Air Force Research Office, the Interdisciplinary University Research Organization is committed to the research of adaptive waveforms and has successfully applied its theoretical results to US radars. In 2007, Sandeep P. Sira et al. proposed a two-step adaptive waveform improvement strategy to suppress range sidelobes in strong sea clutter (sea clutter is the most complex form of radar clutter) to achieve range sidelobe suppression and improve target detection performance.

[0006] Therefore, in areas such as sonar where low interception is required, using low interception waveform improvements to suppress range sidelobes has important theoretical and application value for improving the performance of dense multi-target detection. Summary of the invention

[0007] OFDM waveform has the advantages of high spectrum utilization and strong anti-interference ability, and has been widely used in the fields of communication and radar imaging. Based on the advantage of low interception of OFDM waveform, the present invention realizes the suppression of range sidelobes generated by active detection of densely packed targets through improvement of OFDM waveform.

[0008] On the one hand, the present application provides a method for dense target detection based on low intercept waveform, characterized in that the method comprises:

[0009] The transmitting end generates a low intercept wave signal;

[0010] The low intercept wave signal is added to a cyclic prefix to obtain a low intercept wave with a guard interval inserted to prevent cross-range interference; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by intensive target motion; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units;

[0011] The low intercept waveform inserted into the guard interval to prevent cross-distance interference is modulated by radio frequency and then transmitted to the monitoring area as a detection signal.

[0012] Preferably, the transmitting end randomly generates an initial modulation symbol before generating the low acquisition intercept wave signal, and performs IFFT processing on the initial modulation symbol to obtain the low acquisition intercept wave signal.

[0013] In a second aspect, the present application provides a method for dense target detection based on a low intercept waveform, characterized in that the method comprises:

[0014] The receiving end receives the detection echo signal reflected by the dense target; the detection echo signal includes a low intercept waveform with a guard interval inserted to prevent cross-range interference obtained by adding a cyclic prefix to the low intercept wave signal; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by the movement of the dense target; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units;

[0015] The cyclic prefix is ​​removed from the detection echo signal to eliminate the cross-distance interference between the distance pixel units to obtain multiple independent echo signals without crosstalk between the distance resolution units;

[0016] The multiple independent echo signals are subjected to FFT processing and demodulation, and then subjected to IFFT processing to obtain a distance reconstruction signal for the dense target.

[0017] Preferably, the low intercept wave signal is obtained by randomly generating initial modulation symbols at the transmitting end and performing IFFT processing on the initial modulation symbols.

[0018] Preferably, the interference between the distance pixel units appears in the sampling of the front cyclic prefix length of the detection echo signal, and the sampling point of the front cyclic prefix length needs to be removed.

[0019] In a third aspect, the present application provides a dense target detection device based on a low intercept waveform, characterized in that the device comprises:

[0020] The transmitting end is used to generate a low intercept wave signal, add a cyclic prefix to the low intercept wave signal, and obtain a low intercept waveform with a guard interval inserted to prevent cross-range interference; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by intensive target motion; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units;

[0021] The low intercept waveform inserted into the protection interval to prevent cross-distance interference is transmitted to the monitoring area as a detection signal after being modulated by radio frequency.

[0022] Preferably, the device further comprises:

[0023] The receiving end is used to receive the detection echo signal reflected by the dense target, remove the cyclic prefix of the detection echo signal, eliminate the cross-distance interference between the distance pixel units, and obtain multiple independent echo signals without crosstalk between the distance resolution units; perform FFT processing and demodulation on the multiple independent echo signals, and then perform IFFT processing to obtain the distance reconstruction signal of the dense target.

[0024] Preferably, the transmitting end randomly generates an initial modulation symbol before generating the low acquisition intercept wave signal, and performs IFFT processing on the initial modulation symbol to obtain the low acquisition intercept wave signal.

[0025] Preferably, the interference between the range pixel units occurs in the sampling of the front cyclic prefix length of the detection echo signal, and the sampling points of the front cyclic prefix length need to be removed.

[0026] The present invention utilizes low intercept waveform improvement to achieve range sidelobe suppression, which has important theoretical and application value for improving non-cooperative intensive target detection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more simply illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0028] Figure 1 It is a flow chart of the transmitter of the intensive target detection method based on the low intercept waveform in the embodiment of the present application;

[0029] Figure 2 It is a flow chart of the receiving end of the intensive target detection method based on the low intercept waveform in the embodiment of the present application;

[0030] Figure 3 It is a structural schematic diagram of a dense target detection device based on a low intercept waveform in an embodiment of the present application;

[0031] Figure 4 This is a performance comparison diagram of the dense target detection method based on the low intercept waveform in the embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. The embodiments in the present invention and all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In this embodiment, as an optional method, taking OFDM waveform as an example, a high-resolution distance reconstruction algorithm for non-cooperative (hostile) dense targets is described. The present invention studies OFDM waveforms suitable for multi-target detection systems. On the basis that OFDM waveforms can achieve low interception, a cyclic prefix (CP) of sufficient length is inserted to achieve the advantages of OFDM low sidelobe and interrange cell interference (IRCI) suppression, and an active detection transmitter and receiver working model is constructed to improve the detection performance of dense targets.

[0034] The OFDM waveform is a multi-carrier modulated signal. The use of a large time-bandwidth product transmit signal can cause the enemy receiver to mismatch the transmitted signal in the frequency domain and be unable to identify it, while the friendly side can match the received target echo in the frequency domain, thus effectively preventing the signal from being intercepted by the enemy. In the time domain, the modulated signal is similar to white noise with low peak power, which creates good stealth and noise resistance. In the frequency domain, OFDM technology evenly distributes the energy of the signal throughout the frequency band, with a wide spectrum.

[0035] In addition, OFDM waveform has an important feature: by adding a sufficiently long cyclic prefix CP, a channel with inter-symbol interference (ISI) caused by multipath can be converted into multiple sub-channels without inter-symbol interference. This feature is applied to low interception application scenarios (such as sonar detection), and different range cells can be regarded as different sub-channels, and ISI corresponds to the crosstalk between range resolution cells (IRCI). The transmitter uses an OFDM signal containing a sufficiently long CP, and the receiver separates the echo signals of multiple range cells into multiple independent echo signals without crosstalk between range resolution cells (IRCI-fTee).

[0036] Figure 1 The following is a flow chart of a transmitter of a dense target detection method based on a low intercept waveform in an embodiment of the present application, and the specific steps are as follows:

[0037] Step S110: the transmitting end generates a low intercept wave signal.

[0038] Before the transmitter generates a low-capture wave signal, it is also necessary to randomly generate an initial modulation symbol, and perform IFFT processing on the initial modulation symbol to obtain a low-capture wave signal.

[0039] The discrete OFDM signal model can be expressed as:

[0040]

[0041] Among them, W k (k=0, 1, ..., N-1) is the modulation symbol, corresponding to the complex weight value of the nth subcarrier, The OFDM signal satisfies 1 / T=Δf, where T is the length of the OFDM signal excluding the cyclic prefix (CP), Δf is the carrier spacing, and the sampling interval is T s =T / N=1 / B, N is the number of subcarriers, B is the bandwidth, OFDM signal S=[S(0)S(T s )…S((N-1)T s)] is equivalent to the modulation symbol vector W = [W0 W1 … W N-1 ]’s N-point IFFT.

[0042] Step S120: adding the low intercept wave signal to a cyclic prefix to obtain a low intercept wave signal with a guard interval inserted to prevent cross-range interference; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by intensive target motion; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units.

[0043] For non-cooperative targets, the distance movement caused by target motion will reduce the detection performance of dense targets. By inserting a CP of sufficient length, the present invention proposes a high-resolution distance reconstruction algorithm for non-cooperative dense targets.

[0044] Step S130: The low intercept waveform inserted with the guard interval to prevent cross-distance interference is modulated by radio frequency and then transmitted to the monitoring area as a detection signal.

[0045] Assume that the target scene contains K distance pixel units, Δk is the number of distance pixel offsets caused by target motion, Δk max =max{|Δk|}. To achieve low sidelobe reconstruction at target distance, the interference of all target echoes must be suppressed. When Δk≥0, the length of CP needs to satisfy N CP ≥K+Δk max -1, the echo time delay caused by all target motion will not exceed T CP When Δk<0, the length of the inserted CP must satisfy N CP ≥Δk max The total length of CP is N CP ≥K+2Δk max -1. Compared with the conventional CP-based distance reconstruction, the length of the CP in the present invention needs to consider not only the number of distance units, but also the impact of target motion. Assume R k (t) is the distance from the kth scattering point to the radar, which can be expressed as:

[0046] R k (t) = R k0 +ΔR k ,

[0047] Time delay 2ΔR k / c corresponds to the distance traveled due to motion, which can be approximated as ΔkT s .exist The pulse echo can be approximately expressed as:

[0048]

[0049] in, The OFDM signal with CP inserted can be expressed as:

[0050]

[0051] Figure 2 The following is a flowchart of a receiving end of a method for dense target detection based on a low intercept waveform in an embodiment of the present application. The specific steps are as follows:

[0052] Step S210: the receiving end receives the detection echo signal reflected by the dense target; the detection echo signal includes a low intercept waveform with a guard interval inserted to prevent cross-range interference obtained by adding a cyclic prefix to the low intercept wave signal; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by the movement of the dense target; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units.

[0053] Step S220: removing the cyclic prefix from the detection echo signal, eliminating the cross-range interference between the range pixel units, and obtaining a plurality of independent echo signals without crosstalk between the range resolution units.

[0054] Assume that the echo signal length is N+N CP +K-1, the distance between the units appears in the first N CP In order to suppress the side lobes, the first N samples CP samples need to be removed. At the same time, the last K-1 samples of the removed signal cannot fully reflect the backscattering of the K scattering points in the distance direction. Therefore, at the receiving end, after removing the CP, the last K-1 sampling values ​​need to be removed. The m-th distance echo signal is converted to:

[0055]

[0056] Step S230: performing FFT processing and demodulation on the multiple independent echo signals, and then performing IFFT processing to obtain a distance reconstruction signal for the dense target.

[0057] At the receiving end, the FFT operation is performed on the vector G, and the result is:

[0058]

[0059] Among them, vectors g and u are respectively the vector G and N-point FFT of . is a vector The FFT of is a periodic function with period N, Equivalent to Essentially the vector S of N CP-Δk-point cyclic translation. When there is no Δk term, N for W CP Point translation can be expressed as:

[0060]

[0061] It can be estimated by the following formula:

[0062]

[0063] U can be obtained by performing N-point IFFT on u. Considering the influence of Δk, the distance unit is reconstructed as:

[0064]

[0065] Figure 3 : is a schematic diagram of the structure of a dense target detection device based on a low intercept waveform in an embodiment of the present application, including a transmitting end and a receiving end, as follows:

[0066] The transmitting end 310 is used to generate a low intercept wave signal, add a cyclic prefix to the low intercept wave signal, and obtain a low intercept waveform for preventing cross-range interference with a guard interval inserted; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by intensive target motion; the monitoring area includes multiple range pixel units, and there is cross-range interference between different range pixel units; the low intercept waveform for preventing cross-range interference with a guard interval inserted is transmitted to the monitoring area as a detection signal after radio frequency modulation.

[0067] Before the transmitting end generates the low intercept wave signal, it randomly generates the initial modulation symbol, and performs IFFT processing on the initial modulation symbol to obtain the low intercept wave signal.

[0068] The receiving end 320 is used to receive the detection echo signal reflected by the dense target, remove the cyclic prefix of the detection echo signal, eliminate the cross-distance interference between the distance pixel units, and obtain multiple independent echo signals without crosstalk between the distance resolution units; perform FFT processing on the multiple independent echo signals and demodulate them, and then perform IFFT processing to obtain the distance reconstruction signal of the dense target.

[0069] Interference between range pixel units occurs in the sampling of the front cyclic prefix length of the detection echo signal, and the sampling points of the front cyclic prefix length need to be removed.

[0070] Figure 4 This is a performance comparison diagram of the dense target detection method based on the low intercept waveform in the embodiment of the present application, which verifies the influence of the CP length on the distance reconstruction algorithm.

[0071] Assuming that there are 6 targets evenly distributed in the target scene, and the amplitude of the remaining range unit scattering points is zero, after the distance reconstruction using the method of the present invention, in order to further verify the sidelobe suppression performance of the algorithm, the OFDM detection method with different CP lengths is compared with the traditional LFM range pulse compression method, such as Figure 4 The normalized distance reconstruction results are given. The solid waveform is the result of the traditional method, and the dotted waveform is the result of the method of the present invention. When the CP length is 511, the estimated amplitude result is lower than -330dB in the area where the scattering point amplitude of the method of the present invention is zero. As the CP length decreases, the sidelobe increases. When the CP length is 0, the sidelobe suppression effect is even lower than that of the traditional method. Therefore, only by inserting a CP of sufficient length can the distance reconstruction with low sidelobe be obtained.

[0072] Based on the low interception characteristic of OFDM waveform, the present invention inserts a CP of sufficient length into the OFDM waveform to achieve the purpose of low sidelobe and IRCI suppression of dense target detection waveform, proposes a high-resolution distance reconstruction algorithm for non-cooperative dense targets, studies the OFDM waveform suitable for multi-target detection system, and constructs the working models of the transmitter and the receiver to improve the detection performance of dense targets.

[0073] It should be noted that the method provided herein is not inherently related to any specific computer, virtual device or other equipment. Various general devices can also be used together with the teaching based on this. According to the above description, it is obvious to construct the structure required for this type of device. In addition, the present invention is not directed to any specific programming language. It should be understood that various programming languages ​​can be utilized to implement the present invention described herein, and the description of the call of specific languages ​​and system function modules above is only for the purpose of disclosing the best mode of the invention.

[0074] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be implemented without these specific details. In some examples, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0075] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention belong to the scope of the present invention and its equivalent technology, the present invention is also intended to include these changes and variations.

Claims

1. A method for dense target detection based on low intercept waveform, characterized in that: The method comprises: The transmitting end generates a low intercept wave signal; The low intercept wave signal is added to a cyclic prefix to obtain a low intercept wave with a guard interval inserted to prevent cross-range interference; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by intensive target motion; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units; The low intercept waveform inserted into the guard interval to prevent cross-distance interference is modulated by radio frequency and then transmitted to the monitoring area as a detection signal.

2. The method according to claim 1, characterized in that The transmitting end randomly generates an initial modulation symbol before generating a low acquisition intercept wave signal, and performs IFFT processing on the initial modulation symbol to obtain the low acquisition intercept wave signal.

3. A method for dense target detection based on low intercept waveform, characterized in that: The method comprises: The receiving end receives the detection echo signal reflected by the dense target; the detection echo signal includes a low intercept waveform with a guard interval inserted to prevent cross-range interference obtained by adding a cyclic prefix to the low intercept wave signal; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by the movement of the dense target; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units; The cyclic prefix is ​​removed from the detection echo signal to eliminate the cross-distance interference between the distance pixel units to obtain multiple independent echo signals without crosstalk between the distance resolution units; The multiple independent echo signals are subjected to FFT processing and demodulation, and then subjected to IFFT processing to obtain a distance reconstruction signal for the dense target.

4. The method according to claim 3, characterized in that The low intercept wave signal is obtained by randomly generating an initial modulation symbol at the transmitting end and performing IFFT processing on the initial modulation symbol.

5. The method according to claim 3, characterized in that: The interference between the range pixel units occurs in the sampling of the front cyclic prefix length of the detection echo signal, and the sampling points of the front cyclic prefix length need to be removed.

6. A dense target detection device based on low intercept waveform, characterized in that: The device comprises: The transmitting end is used to generate a low intercept wave signal, add a cyclic prefix to the low intercept wave signal, and obtain a low intercept waveform with a guard interval inserted to prevent cross-range interference; the length of the cyclic prefix is ​​at least the sum of the number of range pixel units included in the monitoring area and the number of range pixel offsets caused by intensive target motion; the monitoring area includes multiple range pixel units, and cross-range interference exists between different range pixel units; The low intercept waveform inserted into the protection interval to prevent cross-distance interference is transmitted to the monitoring area as a detection signal after being modulated by radio frequency.

7. The device according to claim 6, characterized in that The device also includes: The receiving end is used to receive the detection echo signal reflected by the dense target, remove the cyclic prefix of the detection echo signal, eliminate the cross-distance interference between the distance pixel units, and obtain multiple independent echo signals without crosstalk between the distance resolution units; perform FFT processing and demodulation on the multiple independent echo signals, and then perform IFFT processing to obtain the distance reconstruction signal of the dense target.

8. The device according to claim 6, characterized in that The transmitting end randomly generates an initial modulation symbol before generating the low capture wave intercept signal, and performs IFFT processing on the initial modulation symbol to obtain the low capture wave intercept signal.

9. The device according to claim 7, characterized in that The interference between the range pixel units occurs in the sampling of the front cyclic prefix length of the detection echo signal, and the sampling points of the front cyclic prefix length need to be removed.

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