A method and system for suppressing radar multipath interference based on waveform linkage

Abstract

The present invention discloses a method and system for suppressing radar multipath interference based on waveform linkage. The signal processor realizes the real-time transmission of radar signals with modulated alternating waveforms by DDS through parameter configuration and timing control. The signal processor performs matched filtering on the received radar echo signals, and then performs correlation processing on the echo signals of multiple cycles in the range unit. At the same time, a parameterizable auxiliary suppression mode is set, and for multipath interference in complex environments, a mode correction method is used for suppression. Through the timing control and signal processing operations of the signal processor, the present invention realizes the modulation and alternation of the radar transmission waveform, matched filtering, and multi-pulse correlation, achieving the maximum suppression of multipath interference in complex environments, improving the small target detection ability, and increasing the signal-to-noise ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar, and particularly relates to a method and system for suppressing radar multipath interference based on waveform linkage.

Background Art

[0002] The usage environment of radar is becoming more and more harsh. For the background echo in a complex environment, it not only contains target signals, but also clutter, noise and interference. The ideal target echo is the target's primary scattered signal. However, in reality, due to the complex background, some target echoes will be received by the radar after multiple scatterings, that is, the multipath interference of virtual targets is formed. Multipath interference not only affects the detection performance in a single detection, but also forms multiple echoes across cycles in multiple detections, especially obvious in high PRF radars, seriously affecting the detection and recognition performance of the radar. Therefore, it is necessary to find newer and more practical signal processing technologies to improve the radar's anti-multipath interference performance and promote the wide application of this technology in complex environments.

[0003] For conventional radar multipath interference suppression methods, generally, simple PRF modulation and demodulation methods are adopted. For example, a kind of anti-interference method based on inter-pulse pseudo-random code disclosed in the prior art with the patent publication number CN109490851B has a certain effect in an environment with a relatively simple background, but the suppression effect is very limited in a complex environment.

[0004] In some types of radars, time sensitivity control and reducing system gain are also used to reduce the influence of multipath interference. For example, a harmonic radar based on FPGA and deep learning disclosed in the prior art with the patent publication number CN114609593A. However, while suppressing multipath interference, if the suppression intensity is too large, it will cause target loss, especially the loss of small targets. If the suppression intensity is not enough, multipath echoes will remain, and the suppression effect is very poor in a complex environment.

[0005] In order to overcome strong multipath interference, some radars adopt an adaptive multipath interference suppression algorithm based on the least mean square error. For example, a method for suppressing coupled signals of a through-wall radar based on the least mean square error criterion disclosed in the prior art with the patent publication number CN105929375A has a very large amount of computation when calculating the update recursion of the filter weight coefficient, has very high real-time requirements for the engineering software and hardware design, and has a very limited scope of use. At the same time, this method is based on an ideal mathematical model, so its application effect in a complex environment is very limited.

[0006] Therefore, it is necessary to provide a new method for suppressing radar multipath interference based on waveform linkage to solve the above technical problems.

Summary of the Invention

[0007] One of the main objectives of the present invention is to provide a method for suppressing radar multipath interference based on waveform linkage. Through the timing control and signal processing operations of the signal processor, the modulation alternation, matched filtering, and multi-pulse correlation of the radar transmitted waveform are realized, achieving the maximum suppression of multipath interference in complex environments, enhancing the small target detection ability, and improving the signal-to-noise ratio.

[0008] The present invention realizes the above object through the following technical solutions: A method for suppressing radar multipath interference based on waveform linkage, which includes the following steps:

[0009] S1) Through parameter configuration and timing control, based on DDS, synchronously transmit the real-time radar signal s(t) with modulated alternation of the waveform;

[0010]

[0011] where i = 0, 1, 2,... is the pulse sequence, M = 0, when in the auxiliary suppression mode, take M = 1 or M = 2, fix is the floor function; s(t) is a linear frequency modulation pulse signal, τ is the transmitted pulse width, A is the transmitted pulse amplitude, B is the transmitted signal bandwidth, f0 is the transmitted fixed carrier frequency, T r is the pulse repetition period, is the initial phase of the transmitted signal, and j is the imaginary part symbol.

[0012] S2) Under the synchronization of the system timing, based on s(t), generate the impulse response signal h(t) and the scattered echo signal r(t) with timing synchronization, and perform windowed matched filtering processing to obtain the first output signal y(t):

[0013]

[0014] where, is the convolution operation; K(t) is the time-domain product of the echo scattering coefficient and the window function, sinc is the sinc function, f d is the Doppler frequency, is the scattering phase;

[0015] S3) Perform multi-pulse correlation processing on the first output signal y(t) to obtain the second output signal y'(t):

[0016]

[0017] In the formula, y(t + a·T r ) is the output of the multi-period windowed matched filtering processing in step S2), T r is the pulse repetition period, M = 0, when in the auxiliary correction mode, M = 1 or M = 2.

[0018] Another object of the present invention is to provide a system for implementing the above-mentioned radar multipath interference suppression method, which includes a DDS signal generation module for synchronously transmitting a waveform to modulate an alternating real-time radar signal s(t) according to a system clock, and a signal processing module for performing matched filtering processing and multi-pulse correlation processing on the radar scattered echo signal r(t) of the real-time radar signal s(t). The DDS signal generation module includes a parameter configuration module, a synchronous clock module, a first accumulator, a phase register, a second accumulator, a function lookup table, a digital-to-analog converter, a low-pass filter, an up-converter, and a power amplifier; the signal processing module includes a signal preprocessing module, a windowed matched filtering processing module, a data storage module, and a multi-pulse correlation processing module.

[0019] Further, the control method of the DDS signal generation module includes: configuring a frequency control word and a phase control word through the parameter configuration module, and linking the DDS under the synchronization of the system synchronization clock generated by the synchronous clock module. The DDS is composed of the first accumulator and the phase register; the frequency control word is used as one input of the first accumulator, and the output of the phase register is used as the other input of the first accumulator. At each clock trigger, the accumulated result of the first accumulator is stored in the phase register; the data stored in the phase register is added to the phase control word in the second accumulator to form a new phase, and this is used as the address of the function lookup table and stored in the function lookup table. The amplitude values of the waveform are stored in the address of the function lookup table. These discrete amplitude values are processed by the digital-to-analog converter and the low-pass filter to be restored to an analog waveform; after the analog waveform is further processed by the up-converter and the power amplifier, the system can synchronously transmit a waveform to modulate the alternating real-time radar signal s(t).

[0020] Further, the processing method of the windowed matched filtering processing module includes:

[0021] S21) Digital quantization of the synchronously transmitted waveform-modulated alternating real-time radar signal s(t), the radar scattered echo signal r(t) based on s(t), the impulse response signal h(t) based on s(t), the window function signal w(t), the first output signal y(t), and the second output signal y'(t) is performed according to a repetition period to obtain s i (n), r i (n), h i (n), w(n), y i (n), y i '(n), where i = 0, 1, 2,... is a pulse sequence, and n = 0, 1, 2,..., N - 1 is a signal sequence;

[0022] S22) r i (n), hi (n), y i (n) is transformed into a frequency-domain signal R through fast Fourier transform i (k), H i (k), Y i (k);

[0023] S23) Multiply the transmitted signal and the Taylor window function signal of each pulse repetition period through conjugate flipping to generate an impulse response signal h corresponding to each period i (n):

[0024] h i (n) = s i * (N - 1 - n)·w(n) i = 0, 1, 2, …, n = 0, 1, …, N - 1;

[0025] In the formula, s i * () is the complex conjugate of s i (), w(n) is the Taylor window function, and N is the impulse response length;

[0026] S24) Pad zeros to the scattered echo signal r i (n) and the impulse response signal h i (n);

[0027] S25) Perform FFT transformation on the scattered echo signal r i (n) and the impulse response signal h i (n) respectively, and then perform IFFT transformation on the obtained results to restore them to the time-domain output y i (n):

[0028]

[0029] In the formula, FFT is the fast Fourier transform, IFFT is the inverse fast Fourier transform, is the convolution operation; then the signal expression corresponding to y(n) discretized for any repetition period is:

[0030]

[0031] Furthermore, the processing method of the multi-pulse correlation processing module includes: the first output signal y(t) obtained after being processed through the step S2) enters the cache rearrangement module according to the set time sequence, performs data caching and rearrangement according to range cells on the first output signal y(t), and then is sent to the pulse correlation module for processing to obtain the second output signal y'(t).

[0032] Compared with the prior art, the beneficial effects of a radar multipath interference suppression method and system based on waveform linkage according to the present invention are as follows: By means of the linkage between signal processing and DDS waveform generation, the purpose of suppressing multipath is achieved based on a mathematical model, and a good suppression effect is obtained; The echo (target + interference) is subjected to matched filtering and multi-period correlation processing, and the mismatch of multipath interference in the filtering process and the correlation process is utilized to improve the signal-to-interference ratio and signal-to-noise ratio, and the small target detection ability is enhanced; For multipath interference in a complex environment, a parameterizable auxiliary suppression mode is set to correct the effectiveness of interference suppression. Specifically,

[0033] 1) By means of the coordinated operation of the signal processor and DDS, the integration of radar transmitted signal modulation alternation and signal processing is realized, overcoming the limitations of traditional suppression methods based only on post-signal processing, and having better suppression effects and algorithm upgrade capabilities;

[0034] 2) Based on the waveform modulation alternation of controlling DDS and the pulse matching difference between the target and multipath, the signal processor further cascades matched filtering and multi-pulse correlation processing, minimizing the remaining multipath interference in a complex environment, and at the same time improving the detection signal-to-noise ratio of small targets;

[0035] 3) The timing control, parameter configuration and mathematical operations of the signal processor adopt a modular software design based on FPGA. The software is iterable, easy to transplant and upgrade. The engineering implementation has greatly reduced computational complexity and high efficiency; At the same time, the design is flexible, bringing a great improvement in testability and maintainability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the flow block diagram of the present invention;

[0037] Figure 2 is the working block diagram of the signal processor of the present invention linked with DDS;

[0038] Figure 3 is the flow chart of the matched filtering cascaded multi-pulse correlation processing of the present invention;

[0039] Figure 4 is the schematic diagram of the FPGA-based signal processor of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] Example 1:

[0041] Please refer to Figure 1 , which is the flow block diagram of a radar multipath interference suppression method based on waveform linkage provided by a preferred embodiment of the present invention. A radar multipath interference suppression method based on waveform linkage includes the following steps:

[0042] S1) Through parameter configuration and timing control, based on a direct digital frequency synthesizer (DDS), synchronously transmit a modulated alternating real-time radar signal s(t) with a waveform;

[0043]

[0044] where i = 0, 1, 2,... is a pulse sequence, M = 0, when in the auxiliary suppression mode, M = 1 or M = 2 is taken, fix is the floor function; s(t) is a linear frequency modulation pulse signal, τ is the transmitted pulse width, A is the transmitted pulse amplitude, B is the transmitted signal bandwidth, f0 is the transmitted fixed carrier frequency, T r is the pulse repetition period, is the initial phase of the transmitted signal, and j is the imaginary part symbol.

[0045] S2) Under the synchronization of the system timing, based on s(t), generate a timing-synchronized impulse response signal h(t) and a scattered echo signal r(t), and perform windowed matched filtering processing to obtain a first output signal y(t):

[0046]

[0047] where, is the convolution operation; K(t) is the time-domain product of the echo scattering coefficient and the window function, sinc is the sinc function, f d is the Doppler frequency, is the scattering phase;

[0048] S3) Perform multi-pulse correlation processing on the first output signal y(t) to obtain a second output signal y'(t):

[0049]

[0050] In the formula, y(t + a·T r ) is the output of the multi-period windowed matched filtering processing in step S2), T r is the pulse repetition period, M = 0, and when in the auxiliary correction mode, M = 1 or M = 2 is optional.

[0051] Please refer to Figure 1, this embodiment also provides a system for implementing a radar multipath interference suppression method, which includes a DDS signal generation module that synchronously transmits a waveform-modulated alternating real-time radar signal s(t) according to a system clock, and a signal processing module that performs matched filtering processing and multi-pulse correlation processing on the radar scattered echo signal r(t) of the real-time radar signal s(t). The DDS signal generation module includes a parameter configuration module, a synchronous clock module, a first accumulator, a phase register, a second accumulator, a function lookup table, a digital-to-analog converter, a low-pass filter, an upconverter, and a power amplifier; the signal processing module includes a signal preprocessing module, a windowed matched filtering processing module, a data storage module, and a multi-pulse correlation processing module.

[0052] Please refer to Figure 2 , the processing method of the DDS signal generation module is as follows: Configure the frequency control word and phase control word through the parameter configuration module, and link the DDS under the synchronization of the system synchronization clock generated by the synchronous clock module. The DDS is composed of the first accumulator and the phase register; the frequency control word is used as one input of the first accumulator, and the output of the phase register is used as the other input of the first accumulator. At each clock trigger, the accumulated result of the first accumulator is stored in the phase register; the data stored in the phase register is added to the phase control word in the second accumulator to form a new phase, which is used as the address of the function lookup table and stored in the function lookup table. The address of the function lookup table stores the amplitude value of the waveform. These discrete amplitude values are processed by the digital-to-analog converter and the low-pass filter and restored to an analog waveform; this analog waveform is then processed by the upconverter and the power amplifier to realize the system synchronous transmission waveform modulation of the alternating real-time radar signal s(t).

[0053] Please refer to Figure 3 , the processing method of the windowed matched filtering processing module includes:

[0054] S21) Quantize the signals of the synchronous transmission waveform-modulated alternating real-time radar signal s(t), the radar scattered echo signal r(t) based on s(t), the impulse response signal h(t) based on s(t), the window function signal w(t), the first output signal y(t), and the second output signal y'(t) digitally according to the repetition period to obtain s i (n), r i (n), h i (n), w(n), y i (n), y i '(n), where i = 0, 1, 2,... is the pulse sequence, and n = 0, 1, 2,..., N - 1 is the signal sequence;

[0055] S22) ri (n), h i (n), y i (n) is transformed into a frequency-domain signal R through a fast Fourier transform i (k), H i (k), Y i (k);

[0056] S23) Multiply the transmitted signal and the Taylor window function signal of each pulse repetition period by conjugate flipping to generate the impulse response signal h corresponding to each period i (n):

[0057] h i (n) = s i * (N - 1 - n)·w(n) i = 0, 1, 2, …, n = 0, 1, …, N - 1;

[0058] In the formula, s i * () is the complex conjugate of s i (), w(n) is the Taylor window function, and N is the impulse response length;

[0059] The Taylor window function w(n) is:

[0060]

[0061] In the formula, N is the window function length;

[0062] S24) Pad zeros to the scattered echo signal r i (n) and the impulse response signal h i (n);

[0063] S25) Then perform convolution processing, which is carried out in the frequency domain: Perform FFT transforms on the scattered echo signal r i (n) and the impulse response signal h i (n) respectively, and then perform an IFFT transform on the obtained results to restore them to the time-domain output y i (n):

[0064]

[0065] In the formula, FFT is the fast Fourier transform, IFFT is the inverse fast Fourier transform, is the convolution operation;

[0066] Then the signal expression corresponding to the discretized y(n) for any repetition period is:

[0067]

[0068] The first output signal y(t) obtained after the processing of step S2) enters the cache rearrangement module according to the set timing sequence, where the data of the first output signal y(t) is cached and rearranged according to range cells, and then sent to the pulse correlation module for processing to obtain y'(n); the signal expression corresponding to y'(n) discretized for any repetition period is:

[0069]

[0070] Please refer to Figure 4 , this embodiment also provides a signal processor based on FPGA, which is implemented in an engineering manner in the FPGA-based signal processor. A signal processor based on FPGA includes an FPGA, a DDS, an ADC, a DDR, a FLASH, and an MCU located outside the FPGA. Among them, the FPGA is interconnected with the external up / down frequency conversion unit Up / Down Freq Unit through the DDS, the ADC, the synchronous clock syn_clk, and the control signal control. The FPGA exchanges data, stores data, communicates data, and performs task management with the DDR, the FLASH, and the MCU through a bus. The FPGA communicates with the host computer PC through digital interfaces such as an expandable network and a serial port. Inside the FPGA chip, a synchronous clock module, a parameter configuration module, a mode correction module, the windowed matching filtering processing module, and the multi-pulse correlation processing module are provided.

[0071] The above are only some embodiments of the present invention. For those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for suppressing radar multipath interference based on waveform linkage, characterized in that: It includes the following steps: S1) Through parameter configuration and timing control, the real-time radar signal s(t) with waveform modulation alternation is synchronously transmitted based on DDS; where \(i = 0, 1, 2, \cdots\) is the pulse sequence, \(M = 0\), when in the auxiliary suppression mode, \(M = 1\) or \(M = 2\) is taken, fix is the floor function; \(s(t)\) is the chirp pulse signal, \(\tau\) is the transmit pulse width, \(A\) is the transmit pulse amplitude, \(B\) is the transmit signal bandwidth, \(f_0\) is the transmit fixed carrier frequency, \(T\) r is the pulse repetition period, is the initial phase of the transmit signal, and \(j\) is the imaginary part symbol; S2) Under the synchronization of the system timing, the impulse response signal h(t) and the scattered echo signal r(t) with timing synchronization are processed by windowing and matching filtering based on s(t) to obtain the first output signal y(t): Among them is the convolution operation; K(t) is the time-domain product of the echo scattering coefficient and the window function, sinc is the sinc function, f d is the Doppler frequency, is the scattering phase; The windowing matched filtering process comprises: S21) Digital quantization of the real-time radar signal s(t) with modulated alternating synchronous transmission waveform, the radar scattered echo signal r(t) based on s(t), the impulse response signal h(t) based on s(t), the window function signal w(t), the first output signal y(t), and the second output signal y'(t) is performed according to the repetition period to obtain s i (n), r i (n), h i (n), w(n), y i (n), y i '(n), where i = 0, 1, 2, L is the pulse sequence and n = 0, 1, 2, L, N - 1 is the signal sequence; the second output signal y'(t) is the output signal after multi-pulse correlation processing of the first output signal y(t); S22) Transform r i (n), h i (n), y i (n) into frequency-domain signals R i (k), H i (k), Y i (k) through fast Fourier transform; S23) Multiply the transmitted signal and the Taylor window function signal of each pulse repetition period by conjugate flipping to generate the impulse response signal h corresponding to each period i (n): h i (n) = s i * (N - 1 - n)·w(n) i = 0, 1, 2, …, n = 0, 1, … N - 1; where s i * () is the complex conjugate of s i (), w(n) is the Taylor window function, and N is the impulse response length; S24) Zero-pad the scattered echo signal r i (n) and the impulse response signal h i (n) for each repetition period; S25) Perform FFT transformation on the scattered echo signal r i (n) and the impulse response signal h i (n) respectively, and then perform IFFT transformation on the obtained results to restore them to the time-domain output y i (n): where FFT is the fast Fourier transform, IFFT is the inverse fast Fourier transform, is the convolution operation; then the signal expression corresponding to any discretized y(n) with a repeated period is: S3) performing multi-pulse correlation processing on the first output signal y(t) to obtain a second output signal y'(t): where y(t + a·T r ) is the output of the multi-period windowed matched filtering process in step S2), T r is the pulse repetition period, M = 0, M = 1 or M = 2 in the auxiliary correction mode.

2. A system for implementing the radar multipath interference suppression method as described in claim 1, characterized in that: It comprises a DDS signal generating module for transmitting a waveform modulated alternating real-time radar signal s(t) according to a system clock synchronization, and a signal processing module for performing matched filtering and multi-pulse correlation processing on a radar scattered echo signal r(t) of the real-time radar signal s(t). The DDS signal generating module comprises a parameter configuration module, a synchronous clock module, a first accumulator, a phase register, a second accumulator, a function lookup table, a digital-to-analog converter, a low-pass filter, an up-converter and a power amplifier; and the signal processing module comprises a signal preprocessing module, a windowed matched filtering processing module, a data storage module and a multi-pulse correlation processing block.

3. The system for implementing the radar multipath interference suppression method according to claim 2, characterized in that: The control method of the DDS signal generation module includes: configuring the frequency control word and the phase control word through the parameter configuration module, linking the DDS under the synchronization of the system synchronization clock generated by the synchronization clock module, the DDS is composed of the first accumulator and the phase register; the frequency control word is used as an input of the first accumulator, and the output of the phase register is used as another input of the first accumulator. When each clock is triggered, the result of the accumulation of the first accumulator is stored in the phase register; the data stored in the phase register is then added with the phase control word in the second accumulator to form a new phase, and this is used as the address of the function lookup table and stored in the function lookup table. The address of the function lookup table is saved as the amplitude value of the waveform. These discrete amplitude values are restored to analog waveforms after being processed by the digital-to-analog converter and the low-pass filter; after the analog waveform is processed by the up-converter and the power amplifier, the system can realize the synchronous transmission of the real-time radar signal s(t) with waveform modulation alternation.

4. The system for implementing the radar multipath interference suppression method according to claim 2, characterized in that: The windowing matched filter processing module implements the windowing matched filter processing.

5. The system for implementing the radar multipath interference suppression method according to claim 2, characterized in that: The processing method of the multi-pulse correlation processing module includes: the first output signal y(t) obtained after the processing in step S2) enters the cache rearrangement module according to the set timing, caches the first output signal y(t) and rearranges it according to the distance unit, and then sends it to the pulse correlation module for processing to obtain the second output signal y'(t).

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