Radar distance aliasing false target interference suppression method

Abstract

The invention provides an identification, reconstruction and suppression method for radar distance aliasing false targets. Through the double-receiving channel technology based on inter-pulse phase coding, aliasing false targets can be accurately distinguished from real targets, and the limitation of a traditional method in a complex interference environment is overcome. By adopting a false target identification strategy based on Doppler signal statistical parameters, accurate identification and extraction of aliasing false targets can be realized. By adopting an aliasing interference reconstruction and elimination method in a distance Doppler domain, a false target signal can be accurately reconstructed, effective elimination of the false target signal is realized, and a real target signal is reserved, so that the target detection accuracy and robustness under an interference condition are greatly improved. Simulation experiment results verify the effectiveness of the proposed method, and experiment results show that the method has good aliasing false target interference identification and suppression performance, and has high technical and application values in practical engineering.

Description

Technical Field

[0001] The present invention relates to the field of radar detection technology, and in particular to a method for suppressing radar range aliasing false target interference. Background Art

[0002] With the widespread application of radar in electronic countermeasures (ECM) and autonomous driving, LFMCW (Linear Frequency Modulated Continuous Wave) radars are increasingly facing interference issues during target detection. This is particularly true for interference introduced by radar signals transmitting to each other, creating false targets. Because false targets closely resemble real targets, they can easily lead to erroneous target detection results, posing a significant challenge to target detection. In dense traffic environments, or when radars are intentionally jammed by dense false targets, real targets may appear within the same range gate as false targets in the received signal, causing range aliasing between the false and real targets, severely impacting real target detection. While existing radar aliasing false target interference suppression methods have made some progress, most require significant modifications to the radar hardware architecture or rely on additional sensors, resulting in complex implementation, high resource consumption, and limited interference suppression performance. Therefore, designing a solution that can effectively identify and suppress aliased false target interference without excessive hardware modification costs is of great technical and application value for LFMCW radars. Summary of the Invention

[0003] The present invention aims to provide a radar range aliasing false target interference suppression method to solve the above problems.

[0004] The technical solution of the present invention is: a radar range aliasing false target interference suppression method, comprising:

[0005] S1, pulse-to-pulse phase encoding of the transmitted signal and pulse-to-pulse decoding of the received signal;

[0006] S2, range aliasing interference identification based on decoded and undecoded channel echo signals;

[0007] S3, detection and reconstruction of aliased false target interference signals;

[0008] S4, suppression of aliased false target interference signals.

[0009] Preferably, in S1, the radar transmitter adopts the inter-pulse phase coding technology to perform random two-phase coding modulation on the initial phase of each transmission pulse;

[0010] The receiving end receives echo signals through two receiving channels; one channel performs inter-pulse phase decoding on the received multiple pulse echo signals, while the other receiving channel directly performs post-processing.

[0011] Preferably, in S2,

[0012] In the decoding channel echo, since the phase of the real target signal is correlated between multiple pulses, the real target signal can be effectively accumulated and compressed by coherent processing of multiple pulses. However, the coherence of the interference signal in multiple pulses is destroyed due to phase decoding, resulting in the expansion of the interference signal energy in the Doppler spectrum after multi-pulse accumulation, thereby forming interference stripes in the range Doppler domain.

[0013] In the undecoded channel, the multiple pulse echo signals of the real target are random and have lost their correlation because the inter-pulse phases are not decoded. The interference signal comes from the jamming radar transmitter and is not phase-coded. Therefore, after being received by the interfered radar, it maintains good coherence in multiple pulses. After coherent processing, it forms a false target.

[0014] According to the different characteristics of real targets and interference in the decoded channel and the undecoded channel, false target interference can be identified.

[0015] Preferably, in S3,

[0016] By transforming the echoes of the two channels into the range Doppler domain, the statistical parameters of the Doppler signal are used to realize the range cell detection in the presence of range aliasing false target interference.

[0017] After detecting the range unit where the aliased false target is located, the false target is extracted in the range Doppler domain of the undecoded channel echo, and the interference signal received in the decoded channel is reconstructed by the inverse discrete Fourier transform (IDFT) and inter-pulse phase coding sequence.

[0018] Preferably, in S2,

[0019] When the radar system based on dual receiving channels is working,

[0020] At the transmitting end, the initial phase is randomly generated by a binary phase code generator, and the generated initial phase is used to phase modulate each transmitting pulse. The radar transmits the pulse signal after the coded phase modulation.

[0021] At the receiving end, both the target echo and the interference signal are received by two channels. One receiving channel decodes the initial phase of the received signal in each pulse according to the coded modulation phase generated by the transmitting end, while the other channel does not perform phase decoding and directly receives the echo signal for subsequent processing.

[0022] Assume that the linear frequency modulation pulse signal emitted by the interfered radar in the nth pulse period is:

[0023]

[0024] The jamming pulse signal emitted by the jamming radar is:

[0025]

[0026] Among them, (T d ,f0,K0,T p ) represent the pulse width, carrier frequency, frequency modulation slope and pulse repetition period of the radar transmission signal respectively, (A v ,A I ) represent the signal amplitudes emitted by the victim radar and the jammer radar respectively; rect(·) represents the rectangular window function; φ n Indicates the random initial phase modulated by the interfered radar in the nth pulse period:

[0027]

[0028] Among them, ψ n = ±1, n = 1, 2, ..., N, is the random binary phase codeword generated by the phase code generator of the interfered radar, N is the number of pulses transmitted by the radar during the coherent processing period, Φ P =[φ1 φ2 … φ N ] is the phase vector of each transmitted pulse modulation within a coherent processing period (CPI) of the interfered radar;

[0029] At the receiving end, after the decoded receiving channel of the interfered radar undergoes de-skewing and phase decoding of its own transmitted signal, the two-dimensional echo received within one coherent processing cycle is expressed as:

[0030]

[0031] Among them, w c (t n ,t) represents the received noise, and Represent the received target echo and interference signal respectively;

[0032] In the decoding channel's received signal, the random initial phases of multiple transmitted pulse modulations have been demodulated and removed, so the phases of the real target's echo in different pulses maintain good coherence. However, since the received interference pulse signal is not phase-encoded, it will be accompanied by a randomly modulated initial phase after random phase decoding by the interfered radar receiver, resulting in the loss of coherence between multiple pulses of the interference signal. Therefore, after the two-dimensional Fourier transform of the decoding channel's echo signal, the real target signal can be accurately compressed and accumulated in the range-Doppler domain, forming a peak. However, since the interference signal loses coherence in multiple received pulses, after range-Doppler processing, it will form a diffuse interference stripe in the Doppler dimension.

[0033] On the contrary, in the echo of the undecoded channel of the interfered radar, the characteristics of the real target and the interference signal are completely opposite. The received two-dimensional echo signal can be expressed as:

[0034]

[0035] Among them, w c (t n ,t) represents the two-dimensional noise signal received by the undecoded receiving channel, and Respectively represent the target signal and interference signal received by the undecoded channel, and It is given by:

[0036]

[0037] Where ρ and γ represent the amplitude of the scattered signal and the interference signal of the real target received by the interfered radar respectively; t represents the fast time in each pulse repetition period (PRT), and t n =(n-1)T p T represents the slow time series corresponding to multiple pulses within the coherent processing period, n = 1, 2, ..., N. C =NT p represents the coherent processing interval (CPI) of the victim radar; and represent the target signal beat frequency and interference signal beat frequency received in the nth pulse, respectively, where and Represent the time delay of the real target and interference signal respectively, and are calculated as follows: and C is the propagation speed of electromagnetic waves in free space; and is the instantaneous distance between the real target and the jamming radar to the jammed radar at the nth pulse moment, which is calculated as follows: and Among them, R T and R I Respectively represent the initial distances of the real target and the jammer radar to the jammed radar within the coherent processing period; V T and V I are the moving speeds of the target and jamming radar respectively;

[0038] In the undecoded channel echo, after range Doppler processing, the Doppler profile of the real target is expressed as follows:

[0039]

[0040] Among them, σ T represents a constant related to the target backscatter coefficient, Represents the Doppler frequency of the real target; From the above formula, we can see that since the phase of the real target echo signal is modulated by the random initial phase in each received pulse, its echo signal will lose coherence in multiple pulses. After two-dimensional Fourier transform, the signal energy of the real target will be dispersed on the Doppler profile; on the contrary, since the interference signal has good coherence in multiple received pulses, after range Doppler processing, the interference signal will be accurately accumulated and compressed, thereby generating a false target in the RD image; in the undecoded channel, the interference Doppler profile signal after range Doppler processing is expressed by the following formula,

[0041]

[0042] Among them, σ I It represents the amplitude of the interference signal after range Doppler processing. Therefore, according to the above-mentioned characteristic differences between the real target echo signal and the interference signal in the decoded channel and the undecoded channel, the range aliasing false target interference can be identified.

[0043] Preferably, S3 includes:

[0044] S31, range aliasing false target interference detection;

[0045] Assume that in the signal received by the undecoded channel, each CPI consists of N pulses, and the range sampling length of each pulse is M; after two-dimensional Fourier transform, the discrete Doppler spectrum at the mth range gate is expressed as

[0046]

[0047] in, Indicates that on the mth distance gate One-dimensional discrete Doppler spectrum; represents the frequency interval between two discrete Doppler units; assuming and Respectively represent S m The mean and variance of the magnitude of (n),

[0048]

[0049] And define the ratio of the mean and variance of the Doppler signal of each range gate as

[0050]

[0051] When S m(n) When only real targets are included, the mean, variance, and their ratio of the Doppler profile are usually large. If the Doppler profile contains both real targets and aliased false target interference, the mean and variance of the Doppler signal of the range gate are large, but the ratio of the mean to the variance is small. Based on these characteristic differences, the following threshold criteria are used to detect and identify the range gate where the aliased false target interference is located:

[0052]

[0053] Among them, α, β and θ represent the threshold factors for detecting the distance unit where the range aliasing interference is located; when S m (n) When the above threshold condition is met, it indicates that range aliasing false target interference occurs at range gate m; after the aliasing false target interference is detected, preparation is made for subsequent reconstruction and elimination of the aliasing false target interference.

[0054] Preferably, S3 includes:

[0055] S32, reconstruction of range aliasing false target interference; wherein,

[0056] In the undecoded channel range Doppler image, it is assumed that the aliased false target interference is located at the range gate M A Since the energy of the real target is Therefore, by searching for the peak in the Doppler profile of this range gate, the Doppler unit N where the false target is located can be identified. A Once the distance and Doppler gate position of the aliased false target are detected, the false target interference can be extracted from the undecoded channel range-Doppler image and the interference signal in the decoded channel can be reconstructed;

[0057] Since the main lobe of the false target is usually widened, the extraction and reconstruction of the interference signal needs to be Assume that the rectangular window length is W d , can be obtained from The Doppler spectrum vector used to reconstruct the interference is obtained, which can be specifically expressed as:

[0058]

[0059] After extracting the false target signal, the undecoded channel range gate M can be obtained through inverse DFT. A The aliased interference signal at is:

[0060]

[0061] in, Represents the inverse DFT transform; therefore, by further performing pulse phase decoding on the above reconstructed signal, the false target interference signal in the decoding channel is obtained, which can be specifically expressed as,

[0062]

[0063] Preferred S4, including

[0064] Suppression of aliased false target interference signals, after reconstructing the range aliased interference signal, by subtracting the reconstructed interference signal from the decoded channel received signal To achieve the elimination of interference; the elimination of interference is achieved through the following formula,

[0065]

[0066] in, Indicates the decoding channel is located at the range gate M A The received signal at is a pulse sequence after the distance DFT.

[0067] The beneficial effects of the present invention are:

[0068] (1) Through the dual receiving channel technology based on inter-pulse phase coding, the aliased false targets can be accurately distinguished from the real targets, overcoming the limitations of traditional methods in complex interference environments.

[0069] (2) By adopting a false target recognition strategy based on Doppler signal statistical parameters, accurate recognition and extraction of aliased false targets can be achieved.

[0070] (3) By using the aliasing interference reconstruction and elimination method in the range Doppler domain, the false target signal can be accurately reconstructed, the false target signal can be effectively eliminated, and the real target signal can be retained, thereby greatly improving the accuracy and robustness of target detection under interference conditions.

[0071] (4) The simulation experiment results verify the effectiveness of the proposed method. The experimental results show that the method has good aliasing false target interference recognition and suppression performance, and has high technical and application value in practical engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 A schematic flow chart of a method for suppressing radar range aliasing false target interference provided by an embodiment of the present invention;

[0073] Figure 2 A diagram of the radar RF front-end architecture based on inter-pulse phase coding and dual-receive channel technology provided by an embodiment of the present invention;

[0074] Figure 3A flow chart of range aliasing false target recognition, reconstruction, and suppression based on dual receiving channels provided in an embodiment of the present invention;

[0075] Figure 4 Range Doppler (RD) diagram corresponding to the received signal of the interfered radar before and after the pulse-to-pulse phase coding technology is used in the embodiment of the present invention;

[0076] Figure 5 A statistical parameter diagram of the Doppler profile signal within each range gate of an undecoded channel in the range Doppler domain provided by an embodiment of the present invention;

[0077] Figure 6 This is a diagram showing the reconstruction and suppression results of range aliasing interference provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0078] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand and implement the present invention. The embodiments of the present invention are not limited thereto.

[0079] Example 1

[0080] 1. Radar range aliasing false target interference suppression solution based on dual receiving channels

[0081] This invention is a method for suppressing aliasing interference when there is range aliasing false target interference in linear frequency modulated continuous wave (LFMCW) radar. In order to effectively identify and suppress aliased false target signals, in the scheme of the present invention, the radar transmitter adopts inter-pulse phase coding technology and the receiver adopts a dual receiving channel structure. The radar RF front-end architecture based on inter-pulse phase coding and dual receiving channel technology is as follows Figure 2 shown

[0082] like Figure 1 As shown in the figure, based on the above radar RF front-end architecture, the range aliasing false target suppression process includes the following implementation steps:

[0083] (1) Inter-pulse phase encoding of the transmitted signal and inter-pulse decoding of the received signal

[0084] The radar transmitter uses inter-pulse phase coding (IPC) technology, applying random binary-code modulation to the initial phase of each transmitted pulse. The receiver receives echo signals via two channels. One channel performs inter-pulse phase decoding on the multiple received pulse echo signals, while the other channel performs direct post-processing.

[0085] (2) Range aliasing interference identification based on decoded and undecoded channel echo signals

[0086] In the decoded channel echo, the true target signal is effectively accumulated and compressed by coherently processing the multiple pulses, due to the phase correlation between the true target signal and the multiple pulses. However, the interference signal is phase-decoded, which destroys its coherence across the multiple pulses. As a result, after multi-pulse accumulation, the interference signal energy appears to be spread across the Doppler spectrum, forming interference stripes in the range-Doppler domain.

[0087] In an undecoded channel, the multiple pulse echo signals of a real target are random and lose correlation because the inter-pulse phases are not decoded. However, the jamming signal, originating from the jamming radar transmitter, is not phase-coded. Therefore, when received by the jammed radar, it maintains good coherence across multiple pulses. After coherence processing, it becomes a false target.

[0088] According to the above different characteristics of the real target and the interference in the decoded channel and the undecoded channel, the false target interference can be identified.

[0089] (3) Detection and reconstruction of aliased false target interference signals

[0090] By transforming the echoes from both channels into the range-Doppler domain and utilizing statistical parameters of the Doppler signal (such as the ratio of mean to variance), range bin detection is achieved for areas where there are interference from range-aliased false targets. After detecting the range bins where the aliased false targets are located, the false targets are extracted in the range-Doppler domain of the undecoded channel echo. The interference signal received in the decoded channel is then reconstructed using a discrete Fourier transform (DFT) and an interpulse phase coding sequence.

[0091] (4) Suppression of aliased false target interference signals

[0092] Finally, by subtracting the reconstructed interference signal from the echo of the decoding channel, the interference signal can be eliminated from the echo signal of the decoding channel, thereby effectively eliminating and suppressing the interference signal of the aliased false target. 2. Aliased false target recognition principle based on dual receiving channels

[0093] When a dual-receive channel radar system is in operation, a binary phase code generator randomly generates an initial phase at the transmitter end. This initial phase is then used to phase-modulate each transmit pulse. The radar then transmits the coded phase-modulated pulse signal. At the receiver end, both the target echo and the interference signal are received by two channels. One receiving channel decodes the initial phase of the received signal in each pulse based on the coded modulation phase generated by the transmitter end, while the other channel directly receives the echo signal for subsequent processing without performing phase decoding.

[0094] Assume that the linear frequency modulation pulse signal emitted by the interfered radar in the nth pulse period is:

[0095]

[0096] The jamming pulse signal emitted by the jamming radar is:

[0097]

[0098] Where, (T d ,f0,K0,T p ) represent the pulse width, carrier frequency, frequency modulation slope and pulse repetition period of the radar transmission signal respectively, (A v ,A I ) represent the signal amplitudes of the victim radar and the jammer radar respectively. rect(·) represents the rectangular window function. φ n Indicates the random initial phase modulated by the interfered radar in the nth pulse period:

[0099]

[0100] Among them, ψ n = ±1, n = 1, 2, ..., N, is the random binary phase codeword generated by the phase code generator of the interfered radar, N is the number of pulses transmitted by the radar during the coherent processing period, Φ P =[φ1 φ2 … φ N ] is the phase vector of each transmitted pulse modulation within a coherent processing period (CPI) of the interfered radar.

[0101] Therefore, at the receiving end, after the decoded receiving channel of the interfered radar undergoes de-skewing and phase decoding of its own transmitted signal, the two-dimensional echo received within one coherent processing cycle can be expressed as:

[0102]

[0103] Among them, w c (t n ,t) represents the received noise, and Represent the received target echo and interference signal respectively.

[0104] In the decoder channel's received signal, the random initial phases of the multiple transmitted pulses have been demodulated and removed, allowing the true target echo to maintain good phase coherence across different pulses. However, since the received interfering pulse signal is not phase-encoded, it retains a random initial phase after random phase decoding by the victim radar receiver, resulting in a loss of coherence between the multiple interfering signal pulses. Therefore, after performing a two-dimensional Fourier transform on the decoder channel's echo signal, the true target signal can be accurately compressed and accumulated in the range-Doppler domain, forming a peak. However, since the interfering signal loses coherence across multiple received pulses, it forms a diffuse interference band in the Doppler dimension after range-Doppler processing.

[0105] On the contrary, in the echo of the undecoded channel of the interfered radar, the characteristics of the real target and the interference signal are completely opposite. The received two-dimensional echo signal can be expressed as:

[0106]

[0107] Here, w c (t n ,t) represents the two-dimensional noise signal received by the undecoded receiving channel, and Respectively represent the target signal and interference signal received by the undecoded channel, and It can be given by the following formula:

[0108]

[0109] Where ρ and γ represent the amplitude of the scattered signal and the interference signal of the real target received by the interfered radar respectively. t represents the fast time in each pulse repetition period (PRT), and t n =(n-1)T p T represents the slow time series corresponding to multiple pulses within the coherent processing period, n = 1, 2, ..., N. C =NT p Indicates the coherent processing interval (CPI) of the victim radar. and represent the target signal beat frequency and interference signal beat frequency received in the nth pulse, respectively, where and Represent the time delay of the real target and interference signal respectively, and are calculated as follows: and C is the propagation speed of electromagnetic waves in free space. and is the instantaneous distance between the real target and the jamming radar to the jammed radar at the nth pulse moment, which is calculated as follows: and Among them, R T and R I Respectively represent the initial distances of the real target and the jammer radar to the jammed radar within the coherent processing period. T and V I are the moving speeds of the target and jamming radar respectively.

[0110] In the undecoded channel echo, after range Doppler processing, the Doppler profile of the real target can be expressed as follows:

[0111]

[0112] Where σ T represents a constant related to the target backscatter coefficient, Represents the Doppler frequency of the real target. As can be seen from the above formula, since the phase of the real target echo signal is modulated by the random initial phase in each received pulse, its echo signal will lose coherence in multiple pulses. After the two-dimensional Fourier transform, the signal energy of the real target will be dispersed on the Doppler profile. On the contrary, since the interference signal has good coherence in multiple received pulses, after the range Doppler processing, the interference signal will be accurately accumulated and compressed, thereby generating a false target in the RD image. In the undecoded channel, the interference Doppler profile signal after range Doppler processing can be expressed by the following formula,

[0113]

[0114] Where σ I It represents the amplitude of the interference signal after range Doppler processing. Therefore, based on the above-mentioned characteristic differences between the real target echo signal and the interference signal in the decoded channel and the undecoded channel, it is possible to identify range aliasing false target interference.

[0115] To suppress range-aliased false target interference, a feasible approach is to first accurately extract the interference signal in the undecoded channel, reconstruct the signal to obtain the interference signal in the decoded channel, and then eliminate it from the received decoded channel signal. Since the false target interference can be effectively accumulated and focused in the range Doppler image in the undecoded channel, and the focused false target contains most of the energy of the interference signal, the interference signal can be obtained by extracting the false target signal from the range Doppler image of the undecoded channel. After extracting the focused false target signal, the interference signal received in the decoded channel can be reconstructed by using a two-dimensional inverse Fourier transform and the coded phase sequence randomly modulated in each pulse by the interfered radar transmitter, and then eliminated in the decoded channel.

[0116] 3. Range aliasing false target interference detection, reconstruction and suppression methods

[0117] 3.1. Range aliasing false target interference detection

[0118] In order to effectively detect and identify the range gate where the range aliasing false target interference is located in the range Doppler image of the interfered radar, the present invention proposes a method for detecting and identifying aliasing interference in the range Doppler domain using the statistical parameters of the Doppler signal in each range gate.

[0119] Assume that in the signal received by the undecoded channel, each CPI consists of N pulses, and the range sampling length of each pulse is M. After two-dimensional Fourier transform, the discrete Doppler spectrum at the mth range gate can be expressed as

[0120]

[0121] Here, Indicates that on the mth distance gate The one-dimensional discrete Doppler spectrum of represents the frequency interval between two discrete Doppler units. Assume and Respectively represent S m The mean and variance of the magnitude of (n),

[0122]

[0123] And define the ratio of the mean and variance of the Doppler signal of each range gate as

[0124]

[0125] When S m (n) When only true targets are included, the mean, variance, and their ratio of the Doppler profile are usually large. If the Doppler profile contains both true targets and aliased false target interference, the mean and variance of the Doppler signal in the range gate are both large, but the ratio of the mean to the variance is small. Based on these characteristic differences, the following threshold criteria can be used to detect and identify the range gate where the range aliased false target interference is located:

[0126]

[0127] Here, α, β, and θ represent the threshold factors for detecting the range unit where the range aliasing interference is located. m When (n) satisfies the above threshold condition, it indicates that range aliasing false target interference has occurred at range gate m. After the aliasing false target interference is detected, subsequent reconstruction and elimination of the aliasing false target interference can be performed.

[0128] 3.2. Reconstruction of range aliasing false target interference

[0129] In the undecoded channel range Doppler image, it is assumed that the aliased false target interference is located at the range gate M A Since the energy of the real target is Therefore, by searching for the peak in the Doppler profile of this range gate, the Doppler unit N where the false target is located can be identified. A Once the range and Doppler gate position of the aliased false target are detected, the false target interference can be extracted from the undecoded channel range-Doppler image and the interference signal in the decoded channel can be reconstructed.

[0130] Since the main lobe of the false target is usually widened, the extraction and reconstruction of the interference signal needs to be Assume that the rectangular window length is W d , can be obtained from The Doppler spectrum vector used to reconstruct the interference is obtained, which can be specifically expressed as:

[0131]

[0132] After extracting the false target signal, the undecoded channel range gate M can be obtained through inverse DFT. A The aliased interference signal at is:

[0133]

[0134] Here, Represents the inverse DFT transform. Therefore, by further performing pulse phase decoding on the above reconstructed signal, the false target interference signal in the decoding channel can be obtained, which can be specifically expressed as,

[0135]

[0136] 3.3. Suppression of range aliasing false target interference

[0137] After reconstructing the range aliased interference signal, the reconstructed interference signal can be subtracted from the decoded channel received signal. To achieve interference elimination. Interference elimination can be achieved through the following formula,

[0138]

[0139] Here, Indicates the decoding channel is located at the range gate M A The received signal at is a pulse sequence after the distance DFT.

[0140] 4. Range aliasing false target interference suppression process

[0141] like Figure 3 As shown in Figure 1, according to the above principles, the detection, reconstruction and suppression process of range aliasing false targets based on dual receiving channels includes the following four main steps:

[0142] (1) Detection and extraction of range-aliased false target interference signals in undecoded channels

[0143] Using the echo data received from the undecoded channel, two-dimensional coherent accumulation is performed to obtain the range Doppler image of the undecoded channel echo. The accumulated false target interference signal is detected and extracted in the range Doppler image of the undecoded channel for subsequent reconstruction and elimination of the interference signal in the decoded channel.

[0144] (2) Reconstruction of range-aliased false target interference signals in the decoding channel

[0145] Perform a two-dimensional inverse Fourier transform on the extracted false target interference signal to convert it from the frequency domain back to the time domain. In the time domain, use the phase sequence of each pulse modulation to perform phase compensation on the extracted interference signal and reconstruct the false target interference signal in the decoding channel to prepare for subsequent interference elimination.

[0146] (3) Elimination of range aliasing false target interference in the decoding channel

[0147] By using the reconstructed interference signal and performing a differential operation between the decoding channel echo signal and the reconstructed interference signal, the interference signal received in the decoding channel can be eliminated.

[0148] Through the above-mentioned processing of the echo signals of the dual receiving channels, the false target interference caused by range aliasing can be effectively identified, reconstructed and eliminated, which significantly improves the target detection performance and accuracy of the radar and realizes reliable and accurate target detection.

[0149] 5. Simulation experiment verification and analysis

[0150] The effectiveness and accuracy of the method proposed in the present invention were tested and verified using computer simulation testing methods. During the simulation test, the simulation scene included a victim radar, three real targets and one jammer radar. The distances between the three real targets and the victim radar were 50 meters, 100 meters and 150 meters, respectively, and the speeds were 20m / s, 10m / s and 20m / s, respectively. The jammer radar moved at a speed of 40 meters / second and was 200 meters away from the victim radar. The operating parameters of the victim radar and the jammer radar are shown in Table 1. The operating parameters and working timings of the two radars are the same, including carrier frequency, bandwidth, pulse duration and pulse repetition frequency (PRF). The signal-to-interference ratio set during the simulation was -20dB. According to these parameter configurations, first, the two-dimensional echo signals received by the victim radar before and after the use of inter-pulse phase coding technology were simulated and analyzed. Figure 4 The range Doppler (RD) images of the received signals of the jammed radar before and after the pulse-to-pulse phase coding technique is adopted are given.

[0151] Table 1 Simulation parameter settings

[0152] parameter set up Carrier frequency 24GHz bandwidth 760MHz Pulse duration 20us Pulse repetition frequency (PRF) 10kHz Number of coherent pulses 256 Target quantity 3 Target distance 50m,100m,150m Interference radar distance 200m Target speed 20m / s,10m / s,20m / s Jamming radar speed 40m / s Signal-to-Interference Ratio (SIR) -20dB

[0153] Figure 4 In the figure, (a) is the RD image of the received signal when the interfered radar does not adopt the inter-pulse phase coding technology; (b) is the RD image of the received signal when the transmitter of the interfered radar adopts inter-pulse phase coding and the receiver does not perform phase decoding; (c) is the RD image of the received signal after the transmitter of the interfered radar adopts inter-pulse phase coding and the receiver performs phase decoding.

[0154] from Figure 4 (a) As can be seen, when the victim radar does not use interpulse phase coding, the RD image of the received signal displays four peaks, including three real targets and one false target. Because the jamming signal is transmitted one way, the range of the false target overlaps with the range of the second real target. Because the range and Doppler profile of this false target are exactly the same as those of the real target, identifying and eliminating the false target under these conditions is extremely difficult.

[0155] Figure 4(b) shows the RD image received by the victim radar when pulse-to-pulse phase encoding is used at the transmitting end but pulse-to-pulse phase decoding is not performed during reception. As can be seen from the figure, because the victim radar initially modulates a random coding phase with each transmitted pulse and does not perform phase decoding during reception, the echo signals of the true target across multiple pulses lose coherence. Consequently, after multi-pulse accumulation, the true target signal cannot be accurately focused, and the target signal energy appears diffuse in the Doppler profile. Furthermore, in this case, because the received interfering signal maintains good coherence across multiple received pulses, the interference is effectively focused and accumulated after multi-pulse accumulation, resulting in the appearance of a false target in the range-Doppler image.

[0156] Figure 4 (c) shows the RD image obtained by a victim radar using inter-pulse phase encoding during transmission and phase decoding of each pulse during reception. In this case, the phase of the true target signal can maintain good coherence, allowing the multiple pulse echo signals of the true target to be effectively focused and accumulated. In contrast, the multiple pulses of the interference signal lose coherence due to random phase modulation during decoding. Therefore, after multi-pulse accumulation, the interference signal energy appears diffuse in the Doppler profile. In theory, traditional inter-pulse phase encoding techniques can introduce a certain accumulation gain through the above process, thereby improving the detection performance of the true target. However, since the interference signal energy is usually stronger, far exceeding the true target signal, and the corresponding false target overlaps with the second true target range unit in the range unit, the second target is still obscured by the stronger interference energy, resulting in the second true target being missed. Therefore, it is necessary to further eliminate and suppress the range aliasing false targets caused by interference.

[0157] In order to further suppress the range aliasing interference using the proposed solution, it is first necessary to detect and identify the range cells where the aliasing interference is located. Figure 5 The figure shows the statistical parameters of the mean, variance, and mean-to-variance ratio of the Doppler profile corresponding to each range gate of the undecoded channel received signal. It can be clearly seen from the figure that when a range gate contains a real target or a false target, the mean and variance of the Doppler signal corresponding to these range gates are large, but the mean-to-variance ratio is significantly different between real targets and aliased interference. Figure 5As shown in (c), when a range bin contains only true targets, the mean-to-variance ratio of the Doppler profile signal corresponding to that range gate is large. However, the mean-to-variance ratio of the Doppler signal corresponding to a range gate containing range aliasing interference is much lower. Therefore, the significant difference in these statistical parameters corresponding to true targets and range aliasing interference can be used to identify the range gate where the range aliasing interference occurs. In this simulation, the threshold parameters α and β for identifying false target interference were both selected as 80.0 dB, and γ was set to 1.0. Through threshold detection, the range gate where the aliasing interference occurs can be accurately identified.

[0158] Figure 5 Displays the statistical parameters of the Doppler profile signal within each range gate of the undecoded channel in the range-Doppler domain, including (a) mean; (b) variance; and (c) ratio of mean to variance.

[0159] After identifying the range gate where the aliased interference is located, the proposed scheme can be used to reconstruct and eliminate the interference. Figure 6 (a) shows a comparison of the original interference signal and the interference signal reconstructed using this scheme. It is clear from the figure that both the real and imaginary parts of the reconstructed interference signal are highly consistent with the original interference signal. Therefore, the reconstructed interference signal, combined with the coded phase sequence, can be used to further reconstruct the interference signal in the decoding channel echo. By subtracting the reconstructed interference signal from the decoding channel echo signal, the aliased interference signal in the decoding channel echo can be eliminated and suppressed.

[0160] Figure 6 The reconstruction and suppression results of the range aliasing interference using the proposed method. These include: (a) reconstruction of the aliased interference signal; (b) RD image after aliasing interference elimination using the proposed method; and (c) comparison of interference suppression results between the traditional method and the proposed method.

[0161] The RD image after eliminating aliasing interference is as follows Figure 6 (b) is shown. Figure 4 Compared with (c), after the aliasing interference is eliminated using the proposed method, the second real target that overlaps with the false target in distance can be clearly displayed. Figure 6 Figure (c) further shows a comparison of Doppler profiles within a range-aliasing unit after aliasing interference suppression using the traditional inter-pulse phase encoding method and the proposed interference suppression method. The figure clearly shows that with the traditional method, the true target is severely obscured by the strong interfering signal aliased by the same range gate phase. However, after reconstructing and eliminating the aliasing interference using the proposed method, the true target can be clearly seen in the Doppler profile. The proposed method improves the signal-to-interference ratio by approximately 25 dB, significantly improving target detection performance.

[0162] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A radar range aliasing false target interference suppression method, characterized in that: include: S1, pulse-to-pulse phase encoding of the transmitted signal and pulse-to-pulse decoding of the received signal; S2, range aliasing interference identification based on decoded and undecoded channel echo signals; S3, detection and reconstruction of aliased false target interference signals; S4, suppression of aliased false target interference signals.

2. A radar range aliasing false target interference suppression method according to claim 1, characterized in that: In S1, the radar transmitter uses inter-pulse phase coding technology to perform random two-phase coding modulation on the initial phase of each transmitted pulse; The receiving end receives echo signals through two receiving channels; one channel performs inter-pulse phase decoding on the received multiple pulse echo signals, while the other receiving channel directly performs post-processing.

3. The radar range aliasing false target interference suppression method according to claim 1, characterized in that: In S2, In the decoding channel echo, since the phase of the real target signal is correlated between multiple pulses, the real target signal can be effectively accumulated and compressed by coherently processing multiple pulses. However, the interference signal is phase-decoded in multiple pulses, and its coherence in multiple pulses is destroyed, resulting in the expansion of the interference signal energy in the Doppler spectrum after multiple pulses are accumulated, thereby forming an interference stripe in the range Doppler domain. In the undecoded channel, the multiple pulse echo signals of the real target are random and have lost their correlation because the inter-pulse phases are not decoded. The jamming signal comes from the jamming radar transmitter and is not phase-coded. Therefore, after being received by the jammed radar, it maintains good coherence in multiple pulses and forms a false target after coherent processing. According to the different characteristics of real targets and interference in the decoded channel and the undecoded channel, false target interference can be identified.

4. The radar range aliasing false target interference suppression method according to claim 1, characterized in that: In S3, By transforming the echoes of the two channels into the range Doppler domain, the statistical parameters of the Doppler signal are used to realize the range cell detection of the range aliasing false target interference. After detecting the range unit where the aliased false target is located, the false target is extracted in the range Doppler domain of the undecoded channel echo, and the interference signal received in the decoded channel is reconstructed by the inverse discrete Fourier transform (IDFT) and inter-pulse phase coding sequence.

5. The radar range aliasing false target interference suppression method according to claim 3, characterized in that: In S2, When the radar system based on dual receiving channels is working, At the transmitting end, the initial phase is randomly generated by a binary phase code generator, and the generated initial phase is used to phase modulate each transmitting pulse. The radar transmits the pulse signal after the coded phase modulation. At the receiving end, both the target echo and the interference signal are received by two channels. One receiving channel decodes the initial phase of the received signal in each pulse according to the coded modulation phase generated by the transmitting end, while the other channel does not perform phase decoding and directly receives the echo signal for subsequent processing. Assume that the linear frequency modulation pulse signal emitted by the interfered radar in the nth pulse period is: The jamming pulse signal emitted by the jamming radar is: Among them, (T d ,f0,K0,T p ) represent the pulse width, carrier frequency, frequency modulation slope and pulse repetition period of the radar transmission signal respectively, (A v ,A I ) represent the signal amplitudes emitted by the victim radar and the jammer radar respectively; rect(·) represents the rectangular window function; φ n Indicates the random initial phase modulated by the interfered radar in the nth pulse period: Among them, ψ n = ±1, n = 1, 2, ..., N, is the random binary phase codeword generated by the phase code generator of the interfered radar, N is the number of pulses transmitted by the radar during the coherent processing period, Φ P =[φ1 φ2 … φ N ] is the phase vector of each transmitted pulse modulation within a coherent processing period (CPI) of the interfered radar; At the receiving end, after the decoded receiving channel of the interfered radar undergoes de-skewing and phase decoding of its own transmitted signal, the two-dimensional echo received within one coherent processing cycle is expressed as: Among them, w c (t n ,t) represents the received noise, and Represent the received target echo and interference signal respectively; In the decoding channel's received signal, the random initial phases of multiple transmitted pulse modulations have been demodulated and removed, so the phases of the real target's echo in different pulses maintain good coherence. However, since the received interference pulse signal is not phase-encoded, it will be accompanied by a randomly modulated initial phase after random phase decoding by the interfered radar receiver, resulting in the loss of coherence between multiple pulses of the interference signal. Therefore, after the two-dimensional Fourier transform of the decoding channel's echo signal, the real target signal can be accurately compressed and accumulated in the range-Doppler domain, forming a peak. However, since the interference signal loses coherence in multiple received pulses, after range-Doppler processing, it will form a diffuse interference stripe in the Doppler dimension. On the contrary, in the echo of the undecoded channel of the interfered radar, the characteristics of the real target and the interference signal are completely opposite. The received two-dimensional echo signal can be expressed as: Among them, w c (t n ,t) represents the two-dimensional noise signal received by the undecoded receiving channel, and Respectively represent the target signal and interference signal received by the undecoded channel, and It is given by: Where ρ and γ represent the amplitude of the scattered signal and the interference signal of the real target received by the interfered radar respectively; t represents the fast time in each pulse repetition period (PRT), and t n =(n-1)T p T represents the slow time series corresponding to multiple pulses within the coherent processing period, n = 1, 2, ..., N. C =NT p represents the coherent processing interval (CPI) of the victim radar; and represent the target signal beat frequency and interference signal beat frequency received in the nth pulse, respectively, where and Represent the time delay of the real target and interference signal respectively, and are calculated as follows: and C is the propagation speed of electromagnetic waves in free space; and is the instantaneous distance between the real target and the jamming radar to the jammed radar at the nth pulse moment, which is calculated as follows: and Among them, R T and R I Respectively represent the initial distances of the real target and the jammer radar to the jammed radar within the coherent processing period; V T and V I are the moving speeds of the target and jamming radar respectively; In the undecoded channel echo, after range Doppler processing, the Doppler profile of the real target is expressed as follows: Among them, σ T represents a constant related to the target backscatter coefficient, Represents the Doppler frequency of the real target; From the above formula, we can see that since the phase of the real target echo signal is modulated by the random initial phase in each received pulse, its echo signal will lose coherence in multiple pulses. After two-dimensional Fourier transform, the signal energy of the real target will be dispersed on the Doppler profile; on the contrary, since the interference signal has good coherence in multiple received pulses, after range Doppler processing, the interference signal will be accurately accumulated and compressed, thereby generating a false target in the RD image; in the undecoded channel, the interference Doppler profile signal after range Doppler processing is expressed by the following formula, Among them, σ I It represents the amplitude of the interference signal after range Doppler processing. Therefore, according to the above-mentioned characteristic differences between the real target echo signal and the interference signal in the decoded channel and the undecoded channel, the range aliasing false target interference can be identified.

6. The radar range aliasing false target interference suppression method according to claim 4, characterized in that S3 include: S31, range aliasing false target interference detection; Assume that in the signal received by the undecoded channel, each CPI consists of N pulses, and the range sampling length of each pulse is M; after two-dimensional Fourier transform, the discrete Doppler spectrum at the mth range gate is expressed as in, Indicates that on the mth distance gate One-dimensional discrete Doppler spectrum; represents the frequency interval between two discrete Doppler units; assuming and Represents S m The mean and variance of the magnitude of (n), And define the ratio of the mean and variance of the Doppler signal of each range gate as When S m (n) When only real targets are included, the mean, variance, and their ratio of the Doppler profile are usually large. If the Doppler profile contains both real targets and aliased false target interference, the mean and variance of the Doppler signal of the range gate are large, but the ratio of the mean to the variance is small. Based on these characteristic differences, the following threshold criteria are used to detect and identify the range gate where the aliased false target interference is located: Among them, α, β and θ represent the threshold factors for detecting the distance unit where the range aliasing interference is located; when S m (n) When the above threshold condition is met, it indicates that range aliasing false target interference occurs at range gate m; after the aliasing false target interference is detected, preparation is made for subsequent reconstruction and elimination of the aliasing false target interference.

7. The radar range aliasing false target interference suppression method according to claim 4, characterized in that S3 include: S32, reconstruction of range aliasing false target interference; wherein, In the undecoded channel range Doppler image, it is assumed that the aliased false target interference is located at the range gate M A Since the energy of the real target is Therefore, by searching for the peak in the Doppler profile of this range gate, the Doppler unit N where the false target is located can be identified. A Once the distance and Doppler gate position of the aliased false target are detected, the false target interference can be extracted from the undecoded channel range-Doppler image and the interference signal in the decoded channel can be reconstructed; Since the main lobe of the false target is usually widened, the extraction and reconstruction of the interference signal needs to be Assume that the rectangular window length is W d , can be obtained from The Doppler spectrum vector used to reconstruct the interference is obtained, which can be specifically expressed as: After extracting the false target signal, the undecoded channel range gate M can be obtained through inverse DFT. A The aliased interference signal at is: in, Represents the inverse DFT transform; therefore, by further performing pulse phase decoding on the above reconstructed signal, the false target interference signal in the decoding channel is obtained, which can be specifically expressed as, 8. The radar range aliasing false target interference suppression method according to claim 4, characterized in that S4 include: After reconstructing the range aliasing interference signal in the decoding channel, the reconstructed interference signal is subtracted from the received signal of the decoding channel. To achieve the elimination of interference; the elimination of interference is achieved through the following formula, in, Indicates the decoding channel is located at the range gate M A The received signal at is a pulse sequence after the distance DFT.

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