A Costas Coding Based Frequency Hopping Signal Interference Suppression Method and System

Abstract

The present invention discloses a method and system for suppressing interference of Costas-coded frequency-hopping signals. By transmitting Costas-coded frequency-hopping signals through a depth charge homing system, broadband matched filtering is performed on the received target echo signals containing interference to obtain target echo signals with peak characteristics, and signals that do not form relevant peaks are filtered out. Then, a frequency sequence of the target echo signals with peak characteristics is constructed to obtain the frequency sequence of the received signals. The frequency sequence of the received signals and the frequency sequence of the transmitted signals are subjected to coincidence operation to obtain target echo signals without interference, completing interference suppression, realizing low-intercept active detection, effectively anti-interference, having low dependence on hardware, and being simple to implement. The ideal ambiguity function similar to a thumbtack shape and excellent cross-correlation properties inherent in Costas further enhance the anti-reverberation ability of the solution of the present invention in the background of strong reverberation in shallow water.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater acoustic detection, and particularly relates to a method and system for suppressing interference of Costas coded frequency-hopping signals. Background Art

[0002] During the operation of a homing system, it will be affected by various interferences, especially underwater acoustic countermeasure interferences. With the rapid development of target simulation technology, the interference effects of "soft kill" underwater acoustic countermeasure equipment such as noise jammers and acoustic decoys have become prominent, which puts higher requirements on the anti-interference ability of the homing system. For artificial interferences such as decoys, generally, the scale information of the target is discriminated by echo broadening or echo highlights, and the target and interference are identified from the scale difference. On the other hand, the identification and suppression of interference can also be achieved through signal system and waveform design. The waveforms generally used by homing systems for transmission are single-frequency pulse signals (Pulse Continuous Wave, PCW), linear frequency modulation signals (Linear Frequency Modulation, LFM), etc. The generation method of PCW is simple, but the Doppler resolution of single-frequency short pulses is low, and the range resolution of single-frequency long pulses is low. Neither of the two pulses can provide high range and high velocity resolution simultaneously. Although LFM can obtain high range and velocity resolution simultaneously when the linear frequency modulation index and pulse width are large enough, the echo is prone to distortion and the detection difficulty increases. Summary of the Invention

[0003] In view of this, the present invention provides a method and system for suppressing interference of Costas coded frequency-hopping signals, which can simply and efficiently detect target echoes under low signal-to-interference ratio and has a good anti-reverberation effect.

[0004] The specific technical solutions adopted by the present invention are as follows:

[0005] A method for suppressing interference of Costas coded frequency-hopping signals includes:

[0006] The depth charge homing system transmits Costas coded frequency-hopping signals to the detection target and receives the target echo signal containing interference;

[0007] Perform broadband matched filtering on the target echo signal containing interference to obtain a target echo signal with peak characteristics, where the peak characteristics include interference peak characteristics and signal peak characteristics;

[0008] Construct a frequency sequence of the target echo signal with peak characteristics to obtain a received signal frequency sequence;

[0009] Perform coincidence operation on the received signal frequency sequence and the transmitted signal frequency sequence to obtain a target echo signal without interference, and complete interference suppression.

[0010] Further, after obtaining the target echo signal without interference and completing interference suppression, the method further includes:

[0011] Performing background normalization on the target echo signal without interference to obtain the target distance and completing target detection.

[0012] Further, performing broadband matched filtering on the target echo signal with interference to obtain a target echo signal with peak characteristics includes:

[0013] Calculating the ambiguity function of the Costas-coded frequency-hopping signal and calculating the Doppler frequency shift range corresponding to when the ambiguity function drops 3 dB from the peak as the Doppler tolerance;

[0014] Calculating the Doppler frequency shift range of the target echo signal with interference;

[0015] Dividing the Doppler frequency shift range into multiple frequency bands at intervals of the Doppler tolerance, allocating corresponding filters to each of the frequency bands for broadband matched filtering detection to obtain a target echo signal with peak characteristics, wherein the filter matching the target speed has the maximum output.

[0016] Further, calculating the Doppler frequency shift range of the target echo signal with interference includes:

[0017] The upper limit of the Doppler frequency shift range:

[0018]

[0019] The lower limit of the Doppler frequency shift range:

[0020]

[0021] where c is the speed of sound; v 1 is the maximum relative radial velocity between the projectile and the target; v 2 is the minimum relative radial velocity between the projectile and the target; α 1 is the target pitch angle when the relative radial velocity between the projectile and the target is v 1 ; α 2 is the target pitch angle when the relative radial velocity between the projectile and the target is v 2 ; and f is the transmission signal frequency of the homing system of the depth charge.

[0022] Further, constructing the frequency sequence of the target echo signal with peak characteristics to obtain the received signal frequency sequence includes:

[0023] Detecting the frequency components of each frequency band through fast Fourier transform and performing frequency correction according to the detection results;

[0024] The target echo signal with completed frequency correction is subjected to merging processing to obtain a received signal frequency sequence having the same number of sub-pulses as the transmitted signal.

[0025] Further, the received signal frequency sequence and the transmitted signal frequency sequence are subjected to coincidence operation to obtain a target echo signal without interference, including:

[0026] For each frequency component of the received signal frequency sequence and each frequency component of the transmitted signal frequency sequence, perform AND logic operation and sum:

[0027]

[0028] where S is the result of the coincidence operation; is the AND logic operation; f tn is the transmitted signal frequency sequence; f bn is the received signal frequency sequence {f b1 , f b2 ,..., f bn}, and n = 1, 2,..., N is the frequency component, and N is the number of Costas signal sub-pulses;

[0029] Compare the result S of the coincidence operation with a preset threshold value, and output the result passing the threshold value, which is the target echo signal without interference.

[0030] A Costas coding frequency hopping signal interference suppression system includes:

[0031] A signal receiving module, configured to receive a target echo signal with interference after a depth charge homing system transmits a Costas coding frequency hopping signal to a detection target;

[0032] A matched filtering module, configured to perform broadband matched filtering on the target echo signal with interference to obtain a target echo signal having peak characteristics, where the peak characteristics include interference peak characteristics and signal peak characteristics;

[0033] A frequency sequence construction module, configured to construct a frequency sequence of the target echo signal having peak characteristics to obtain a received signal frequency sequence;

[0034] A coincidence operation module, configured to perform a coincidence operation on the received signal frequency sequence and the transmitted signal frequency sequence to obtain a target echo signal without interference, and complete interference suppression.

[0035] Further, it further includes:

[0036] A normalization module, configured to perform background normalization on the target echo signal without interference to obtain a target distance and complete target detection.

[0037] Further, the matched filtering module includes:

[0038] A tolerance calculation unit, configured to calculate the ambiguity function of the Costas coded frequency hopping signal, and calculate the Doppler frequency shift range corresponding to when the ambiguity function drops 3 dB from the peak as the Doppler tolerance;

[0039] A frequency shift range calculation unit, configured to calculate the Doppler frequency shift range of the target echo signal with interference;

[0040] A filtering detection unit, configured to divide the Doppler frequency shift range into multiple frequency bands at intervals of the Doppler tolerance, allocate corresponding filters to each of the frequency bands for wideband matched filtering detection, and obtain a target echo signal with peak characteristics, wherein the filter matching the target speed has the maximum output.

[0041] Further, the coincidence operation module includes:

[0042] An operation unit, configured to perform an AND logic operation and sum on the frequency components of each received signal frequency sequence and the frequency components of each transmitted signal frequency sequence:

[0043]

[0044] wherein, S is the result of the coincidence operation; is the AND logic operation; f tn is the transmitted signal frequency sequence; f bn is the received signal frequency sequence {f b1 , f b2 ,..., f bn}, and n = 1, 2,..., N are the frequency components, and N is the number of Costas signal sub-pulses;

[0045] A threshold detection unit, configured to compare the result S of the coincidence operation with a preset threshold value, and output the result of passing the threshold as the target echo signal without interference.

[0046] Beneficial effects:

[0047] (1) A method for suppressing interference of Costas - coded frequency - hopping signals. The Costas - coded frequency - hopping signals are transmitted through the homing system of depth charges. The received target echo signals containing interference are subjected to broadband matched filtering to obtain target echo signals with peak characteristics, and the signals that do not form relevant peaks are filtered out. Then, the frequency sequence of the target echo signals with peak characteristics is constructed to obtain the received signal frequency sequence. The received signal frequency sequence and the transmitted signal frequency sequence are subjected to coincidence operation to obtain target echo signals without interference, completing interference suppression, realizing low - intercept active detection, effectively anti - jamming, having low dependence on hardware, and being easy to implement. The ideal ambiguity function similar to a thumbtack and the superior cross - correlation properties of Costas itself further enhance the anti - reverberation ability of the solution of the present invention in the background of strong reverberation in shallow water.

[0048] (2) By performing background normalization on the target echo signals without interference, the target distance can be clearly obtained, and target detection is completed while strong interference is suppressed.

[0049] (3) With the Doppler tolerance as the interval, the Doppler frequency - shift range is divided into multiple frequency bands, and corresponding filters are assigned to each frequency band for broadband matched - filtering detection. By realizing broadband matched - filtering detection, a better filtering effect can be obtained. And the received signals are divided into different frequency bands and filtered one by one, making the finally obtained echo signals more accurate.

[0050] (4) By detecting the frequency components of each frequency band through fast Fourier transform and performing frequency correction according to the detection results, and then performing merging processing, the interference - suppression ability is further improved, making the final target distance more accurate. Description of the Drawings

[0051] Figure 1 is a flowchart of the interference - suppression method according to an embodiment of the present invention;

[0052] Figure 2 is a structural block diagram of the interference - suppression system according to an embodiment of the present invention;

[0053] Figure 3 is a schematic diagram of the detection result of the received target echo signals after broadband matched - filtering;

[0054] Figure 4 is a schematic diagram of the detection result of the signals after broadband matched - filtering through frequency - diversity coincidence detection;

[0055] Figure 5 is a schematic diagram of the background - normalization result. Detailed Embodiments

[0056] A method and system for suppressing interference of Costas-coded frequency-hopping signals. The Costas-coded frequency-hopping signals are transmitted by a depth charge homing system, and the received target echo signals containing interference are subjected to broadband matched filtering to obtain target echo signals with peak characteristics, and the signals that do not form relevant peaks are filtered out. Then, a frequency sequence of the target echo signals with peak characteristics is constructed to obtain the received signal frequency sequence, and the received signal frequency sequence and the transmitted signal frequency sequence are subjected to coincidence operation to obtain target echo signals without interference, completing interference suppression, realizing low-intercept active detection, being effectively anti-interference, having low dependence on hardware, and being simple to implement. The Costas itself has an ideal ambiguity function close to a thumbtack shape and excellent cross-correlation properties, which further enhances the anti-reverberation ability of the solution of the present invention in the background of strong reverberation in shallow water. Background normalization is performed on the target echo signals without interference, and the target distance can be clearly obtained, and target detection is completed while strong interference is suppressed.

[0057] The following examples are given in conjunction with the accompanying drawings to describe the present invention in detail.

[0058] An embodiment of the present invention provides a method for suppressing interference of Costas-coded frequency-hopping signals, Figure 1 which is a flowchart of the interference suppression method according to an embodiment of the present invention, as Figure 1 shown, and the process includes the following steps:

[0059] Step 1: The depth charge homing system transmits Costas-coded frequency-hopping signals to the detection target and receives the target echo signals containing interference;

[0060] Step 2: Perform broadband matched filtering on the target echo signals containing interference to obtain target echo signals with peak characteristics, where the peak characteristics include interference peak characteristics and signal peak characteristics;

[0061] In a specific embodiment, performing broadband matched filtering on the target echo signals containing interference to obtain target echo signals with peak characteristics includes: calculating the ambiguity function of the Costas-coded frequency-hopping signals, and calculating the Doppler frequency shift range corresponding to when the ambiguity function drops by 3 dB from the peak as the Doppler tolerance; calculating the Doppler frequency shift range of the target echo signals containing interference; dividing the Doppler frequency shift range into multiple frequency bands at intervals of the Doppler tolerance, and allocating corresponding filters to each frequency band for broadband matched filtering detection to obtain target echo signals with peak characteristics, where the filter matching the target speed has the maximum output.

[0062] In a specific embodiment, calculating the Doppler frequency shift range of the target echo signals containing interference includes:

[0063] The upper limit of the Doppler frequency shift range:

[0064]

[0065] Lower limit of Doppler frequency shift range:

[0066]

[0067] where c is the speed of sound; v 1 is the maximum relative radial velocity between the projectile and the target; v 2 is the minimum relative radial velocity between the projectile and the target; α 1 is the target pitch angle when the relative radial velocity between the projectile and the target is v 1 ; α 2 is the target pitch angle when the relative radial velocity between the projectile and the target is v 2 ; f is the transmission signal frequency of the homing system of the depth charge.

[0068] Step 3: Construct a frequency sequence of the target echo signal with peak characteristics to obtain the received signal frequency sequence;

[0069] In a specific embodiment, constructing a frequency sequence of the target echo signal with peak characteristics to obtain the received signal frequency sequence includes: detecting the frequency components of each frequency band through fast Fourier transform and performing frequency correction according to the detection results; performing a merging process on the target echo signal after frequency correction to obtain a received signal frequency sequence with the same number of sub-pulses as the transmission signal.

[0070] Step 4: Perform a coincidence operation on the received signal frequency sequence and the transmission signal frequency sequence to obtain a target echo signal without interference, thereby completing interference suppression.

[0071] In a specific embodiment, performing a coincidence operation on the received signal frequency sequence and the transmission signal frequency sequence to obtain a target echo signal without interference includes:

[0072] Performing an AND logic operation and summing the frequency components of each received signal frequency sequence and the frequency components of each transmission signal frequency sequence:

[0073]

[0074] where S is the result of the coincidence operation; is the AND logic operation; f tn is the transmission signal frequency sequence; f bn is the received signal frequency sequence {f b1 , f b2 ,..., f bn}, and n = 1, 2,..., N are the frequency components, where N is the number of sub-pulses of the Costas signal;

[0075] Compare the result S of the coincidence operation with a preset threshold value, and output the result exceeding the threshold value, which is the target echo signal without interference.

[0076] In a specific embodiment, after obtaining the target echo signal without interference and completing interference suppression, the method further includes: Step Five, perform background normalization on the target echo signal without interference to obtain the target distance and complete target detection.

[0077] The embodiment of the present invention also provides a Costas code frequency-hopping signal interference suppression system. Figure 2 It is a structural block diagram of the interference suppression system according to the embodiment of the present invention, as Figure 2 shown. The interference suppression system includes:

[0078] A signal receiving module, configured to receive the target echo signal with interference after the depth charge homing system transmits a Costas code frequency-hopping signal to the detection target;

[0079] A matched filtering module, configured to perform broadband matched filtering on the target echo signal with interference to obtain a target echo signal with peak characteristics, where the peak characteristics include interference peak characteristics and signal peak characteristics;

[0080] In a specific embodiment, the matched filtering module includes: a tolerance calculation unit, configured to calculate the ambiguity function of the Costas code frequency-hopping signal and calculate the Doppler frequency shift range corresponding to the ambiguity function dropping 3 dB from the peak as the Doppler tolerance; a frequency shift range calculation unit, configured to calculate the Doppler frequency shift range of the target echo signal with interference; a filtering detection unit, configured to divide the Doppler frequency shift range into multiple frequency bands at intervals of the Doppler tolerance, allocate corresponding filters for each frequency band for broadband matched filtering detection, and obtain a target echo signal with peak characteristics, where the filter matching the target speed has the maximum output.

[0081] A frequency sequence construction module, configured to construct a frequency sequence of the target echo signal with peak characteristics to obtain a received signal frequency sequence;

[0082] A coincidence operation module, configured to perform a coincidence operation on the received signal frequency sequence and the transmitted signal frequency sequence to obtain a target echo signal without interference and complete interference suppression.

[0083] In a specific embodiment, the coincidence operation module includes: an operation unit, configured to perform a logical AND operation and sum on the frequency components of each received signal frequency sequence and the frequency components of each transmitted signal frequency sequence:

[0084]

[0085] where S represents the result of the coincidence operation; is a logical operation; f tn is the transmitted signal frequency sequence; f bn is the received signal frequency sequence {f b1 , f b2 ,..., f bn}, where n = 1, 2,..., N are the frequency components, and N is the number of Costas signal sub-pulses;

[0086] The threshold detection unit is used to compare the result S of the coincidence operation with a preset threshold value, and the output result exceeding the threshold is the target echo signal without interference.

[0087] In a specific embodiment, it further includes: a normalization module for performing background normalization on the target echo signal without interference to obtain the target distance and complete target detection.

[0088] In order to enable those skilled in the art to better understand the technical solution of the present invention, the following will be described in conjunction with specific scenario embodiments.

[0089] Scenario Embodiment 1

[0090] In this scenario embodiment, a specific ambiguity function is given, and the signal processing results of each step are shown and explained, and the signal change situation in the processing steps of the present invention can be clearly seen. In this scenario embodiment, a signal with a signal-to-interference ratio of -14 dB is used.

[0091] S1. Wideband matched filtering

[0092] It is divided into the following steps:

[0093] 1) Calculate the ambiguity function of the signal

[0094] The ambiguity function of the Costas coded frequency hopping signal is:

[0095]

[0096] In the formula: N is the number of Costas coded frequency hopping signal sub-pulses; T r is the sub-pulse repetition period; T is the sub-pulse width; c m and c n are the Costas coding serial numbers; Δf is the unit frequency modulation amount, generally taking Δf = 1 / T; τ is the delay time; ξ is the Doppler frequency shift, n ∈ N, m ∈ N, and j represents an imaginary number.

[0097] Substituting the parameters of the Costas signal transmitted by the homing system into the above formula, the ambiguity function of the signal can be obtained.

[0098] 2) Doppler tolerance calculation

[0099] Calculate the Doppler frequency shift range corresponding to the 3 dB drop from the peak of the ambiguity function of the Costas signal emitted by the homing system. This range is the Doppler tolerance.

[0100] 3) Doppler frequency shift calculation

[0101] Let the maximum relative radial velocity between the missile and the target be v 1 , and the minimum relative radial velocity between the missile and the target be v 2 , then the upper and lower limits of the Doppler frequency shift are:

[0102]

[0103]

[0104] where: c is the speed of sound; α 1 is the target elevation angle when the relative radial velocity between the missile and the target is v 1 ; α 2 is the target elevation angle when the relative radial velocity between the missile and the target is v 2 ; f is the frequency of the signal emitted by the homing system.

[0105] 4) Design a wideband matched filter bank

[0106] Divide the Doppler frequency shift range into several frequency bands at intervals of the Doppler tolerance, and generate a corresponding set of matched filter banks.

[0107] 5) Matched filtering detection of received signals

[0108] Independently perform wideband matched filtering detection on the received signals. Among them, the filter that matches the target speed has the maximum output.

[0109] Figure 3 is a schematic diagram of the result of wideband matched filtering detection of the received target echo signal. As Figure 3 shown, the signal includes interference signals (interference) and target signals (signals).

[0110] S2. Frequency diversity coincidence detection

[0111] It is divided into the following steps:

[0112] 1) Frequency search and correction of received signals

[0113] Detect each frequency component of the frequency diversity signal through Fast Fourier Transform (FFT). Considering the possible Doppler frequency shift range of the target, perform peak detection on the FFT result of the received signal within the Doppler frequency shift range, and estimate the received signal frequency f according to the peak detection result. b , and perform frequency correction.

[0114] 2) Construct the frequency sequence

[0115] Merge and process the received signal frequencies to obtain a frequency sequence {f b1 , f b2 ,..., f bn} with the same number as the number of transmitted signals, where n = 1, 2,..., N and N is the number of Costas signal sub-pulses.

[0116] 3) Perform the received and transmitted frequency coincidence operation

[0117] Perform a frequency coincidence operation (perform an AND logic operation on each frequency component and then sum) on the received signal frequency sequence and the transmitted signal frequency sequence. The result is:

[0118]

[0119] In the formula: is the AND logic operation; f tn is the transmitted signal frequency sequence.

[0120] 4) Perform threshold crossing detection

[0121] Compare the result S of the frequency coincidence operation with the threshold value and output the result of crossing the threshold.

[0122] Figure 4 is a schematic diagram of the result of frequency diversity coincidence detection after broadband matched filtering. As Figure 4 shown, only the target signal remains, and the interference signal has been suppressed and filtered out.

[0123] S3. Background normalization

[0124] Perform background normalization on the result of frequency diversity coincidence detection to achieve target detection.

[0125] Figure 5 is a schematic diagram of the background normalization result. As Figure 5 shown, the target distance can be clearly seen, indicating that the present invention realizes target signal detection at a signal-to-interference ratio of -14 dB and suppresses strong interference.

[0126] In summary, the present invention provides a method and system for suppressing interference of Costas-coded frequency-hopping signals. By utilizing the near-thumbtack-shaped ideal ambiguity function and superior cross-correlation properties inherent in Costas, interference suppression is achieved through wideband matched filtering and frequency diversity coincidence detection processing, followed by background normalization of the coincidence-detected signals.

[0127] The present invention solves the limitations of anti-reverberation and anti-interference of the existing transmitting waveforms of homing systems in the shallow sea reverberation background. It has passed the lake anti-interference test verification and can detect target echoes at a low signal-to-interference ratio. The present invention transmits Costas-coded frequency-hopping signals through the homing system, and adopts wideband matched filtering and frequency diversity coincidence detection methods to achieve interference suppression. It can not only achieve low-intercept active detection, but also effectively resist interference. It has a low dependence on hardware, is simple to implement, and the near-thumbtack-shaped ideal ambiguity function enables the present invention to have better anti-reverberation ability in the shallow sea strong reverberation background.

[0128] The above specific embodiments only describe the design principles of the present invention. The shapes and names of the components in this description can be different and are not limited. Therefore, those skilled in the art of the present invention can modify or equivalently replace the technical solutions recorded in the foregoing embodiments; and these modifications and replacements do not depart from the spirit and technical solutions of the present invention, and shall all fall within the protection scope of the present invention.

Claims

1. A method for suppressing interference of Costas - coded frequency - hopping signals, characterized in that, it includes: The depth charge homing system transmits Costas - coded frequency - hopping signals to the detected target and receives the target echo signals containing interference; Perform broadband matched filtering on the target echo signals containing interference to obtain target echo signals with peak characteristics, where the peak characteristics include interference peak characteristics and signal peak characteristics; Construct the frequency sequence of the target echo signals with peak characteristics to obtain the received signal frequency sequence; Perform coincidence operation on the received signal frequency sequence and the transmitted signal frequency sequence to obtain target echo signals without interference, thus completing interference suppression.

2. The method according to claim 1, characterized in that, after obtaining the target echo signals without interference and completing interference suppression, the method further includes: Perform background normalization on the target echo signals without interference to obtain the target distance and complete target detection.

3. The method according to claim 1, characterized in that, Performing broadband matched filtering on the target echo signals containing interference to obtain target echo signals with peak characteristics includes: Calculate the ambiguity function of the Costas - coded frequency - hopping signal, and calculate the Doppler frequency - shift range corresponding to when the ambiguity function drops by 3 dB from the peak as the Doppler tolerance; Calculate the Doppler frequency - shift range of the target echo signals containing interference; Divide the Doppler frequency - shift range into multiple frequency bands at intervals of the Doppler tolerance, and assign corresponding filters to each frequency band for broadband matched filtering detection to obtain target echo signals with peak characteristics, where the filter matching the target speed has the maximum output.

4. The method according to claim 3, characterized in that, Calculating the Doppler frequency - shift range of the target echo signals containing interference includes: The upper limit of the Doppler frequency - shift range: The lower limit of the Doppler frequency - shift range: where c is the speed of sound; v 1 is the maximum relative radial velocity between the projectile and the target; v 2 is the minimum relative radial velocity between the projectile and the target; α 1 is the pitch angle of the target when the relative radial velocity between the projectile and the target is v 1 ; α 2 is the pitch angle of the target when the relative radial velocity between the projectile and the target is v 2 ; f is the transmission signal frequency of the homing system of the depth charge.

5. The method according to claim 1, characterized in that, Constructing the frequency sequence of the target echo signals with peak characteristics to obtain the received signal frequency sequence includes: Detect the frequency components of each frequency band through fast Fourier transform and perform frequency correction according to the detection results; Perform merging processing on the target echo signals after frequency correction to obtain a received signal frequency sequence with the same number of sub - pulses as the transmitted signal.

6. The method according to claim 1, characterized in that, Performing coincidence operation on the received signal frequency sequence and the transmitted signal frequency sequence to obtain target echo signals without interference includes: Perform AND logic operation and sum on the frequency components of each received signal frequency sequence and the frequency components of each transmitted signal frequency sequence: Among them, S is the result of the compliance operation; is the AND logic operation; f tn is the transmitted signal frequency sequence; f bn is the received signal frequency sequence {f b1 , f b2 ,..., f bn}, where n = 1, 2,..., N are the frequency components, and N is the number of Costas signal sub-pulses; Compare the result S of the coincidence operation with a preset threshold value, and output the result passing the threshold value as the target echo signal without interference.

7. A system for suppressing interference of Costas - coded frequency - hopping signals, characterized in that, it includes: A signal receiving module, used to receive target echo signals containing interference after the depth charge homing system transmits Costas - coded frequency - hopping signals; A matched filtering module, which is used to perform broadband matched filtering on the target echo signal with interference to obtain a target echo signal with peak characteristics, where the peak characteristics include interference peak characteristics and signal peak characteristics; A frequency sequence construction module, which is used to construct the frequency sequence of the target echo signal with peak characteristics to obtain a received signal frequency sequence; A coincidence operation module, which is used to perform coincidence operation on the received signal frequency sequence and the transmitted signal frequency sequence to obtain a target echo signal without interference, thereby completing interference suppression.

8. The system according to claim 7, wherein, it further includes: A normalization module, which is used to perform background normalization on the target echo signal without interference to obtain the target distance, thereby completing target detection.

9. The system according to claim 7, wherein, the matched filtering module includes: A tolerance calculation unit, which is used to calculate the ambiguity function of the Costas coded frequency hopping signal and calculate the Doppler frequency shift range corresponding to the 3dB drop from the peak of the ambiguity function as the Doppler tolerance; A frequency shift range calculation unit, which is used to calculate the Doppler frequency shift range of the target echo signal with interference; A filtering detection unit, which is used to divide the Doppler frequency shift range into multiple frequency bands at intervals of the Doppler tolerance, allocate corresponding filters to each frequency band for broadband matched filtering detection, and obtain a target echo signal with peak characteristics, where the filter matched with the target speed has the maximum output.

10. The system according to claim 7, wherein, the coincidence operation module includes: An operation unit, which is used to perform AND logic operation and summation on the frequency components of each received signal frequency sequence and the frequency components of each transmitted signal frequency sequence; Among them, S is the result of the coincidence operation; is the AND logic operation; f tn is the transmitted signal frequency sequence; f bn is the received signal frequency sequence {f b1 , f b2 ,..., f bn}, where n = 1, 2,..., N are the frequency components, and N is the number of Costas signal sub-pulses; A threshold detection unit, which is used to compare the result S of the coincidence operation with a preset threshold value, and output the result passing the threshold as the target echo signal without interference.

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