A wideband transmitting narrowband coherent processing method based on centralized MIMO

Abstract

The application belongs to the field of low-interception MIMO radar signal processing, and particularly relates to a wide-band transmission narrow-band coherent processing method based on centralized MIMO; S1: obtaining the position and speed of a target at a previous moment; S2: selecting multiple position points in a preset range of the position and speed based on the position and speed of the target at the previous moment; S3: calculating the signal-to-noise ratio of the position and speed of the multiple position points; S4: selecting the CFAR detection result with the largest signal-to-noise ratio as the distance and speed of the target; under the condition that the frequency difference between the transmission signals is greater than the bandwidth, the application realizes narrow-band coherent processing through phase compensation and Doppler compensation. By increasing the frequency difference between the transmission signals, the transmission signals are received by different channels of the interception receiver, the energy of the radar transmission signals received by a single channel is reduced, and on the basis of the traditional MIMO radar signal processing, the phase difference compensation and Doppler compensation caused by the different frequencies of the transmission signals are increased, so that target detection is realized.

Description

Technical Field

[0001] This application belongs to the field of low intercept MIMO radar signal processing, and specifically relates to a broadband transmit narrowband coherent processing method based on centralized MIMO. Background Technology

[0002] MIMO radar is a type of radar that can transmit orthogonal waveforms. Both its receiver and transmitter employ multiple-transmitter / receive devices, leveraging the advantages of digital array technology. Each subarray at the transmitter emits mutually orthogonal signals. Because the signals are orthogonal, no beam is formed in space, thus ensuring effective spatial coverage. The waveform diversity capability of MIMO radar gives it significant advantages in low intercept, anti-jamming, anti-clutter, and target identification. Therefore, MIMO radar is widely used in many fields, including ground-based, shipborne, and airborne applications.

[0003] In commonly used MIMO radars, the center frequencies of all transmitted signals are the same, or the frequency spacing is the same as the signal bandwidth, resulting in a relatively strong radar transmitted signal received by the interceptor on a single channel. Therefore, increasing the frequency difference between transmitted signals, so that each transmitted signal is received by the interceptor on different channels, and reducing the energy of the radar transmitted signal received on a single channel, is more conducive to achieving low intercept detection. Therefore, designing a coherent processing method to implement coherent processing when the frequency difference between transmitted signals is greater than the signal bandwidth has practical application value. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a broadband transmit narrowband coherent processing method based on centralized MIMO:

[0005] Step S1: Obtain the target's position and velocity at the previous moment.

[0006] Step S2: Based on the target's position and velocity at the previous moment, select multiple position points within a preset range of the position and velocity;

[0007] Step S3: Calculate the signal-to-noise ratio of the position and velocity at the plurality of location points;

[0008] Step S4: Select the CFAR detection result with the highest signal-to-noise ratio as the target's distance and velocity.

[0009] Preferably, the method for calculating the signal-to-noise ratio includes:

[0010] Step S11: Based on the center frequency of the MIMO radar transmitted signal, down-convert the full array received signal to obtain the baseband echo signal;

[0011] Step S12: Based on each transmitted baseband signal, perform matched filtering on the corresponding baseband echo signal of each array element to obtain the matched filtered signal; wherein, the MIMO radar transmitted signal is obtained by up-converting the transmitted baseband signal;

[0012] Step S13: Perform phase compensation on the matched filter signal, perform Doppler compensation on the phase-compensated signal; sum the Doppler-compensated signals; perform coherent accumulation on the summed signals;

[0013] Step S14: Perform target detection on the coherently accumulated signal; calculate the signal-to-noise ratio of the location points that meet the preset requirements in the detection results.

[0014] Preferably, the phase compensation method includes: calculating the time delay between the multiple location points and the phase center of each transmitting subarray and each receiving array element, and performing phase compensation on the echo signal according to the calculated time delay and the center frequency of each transmitted signal.

[0015] Preferably, the Doppler compensation method includes: calculating the available Doppler frequency based on the velocity of the location point and the center frequency of each transmitted signal, and performing Doppler compensation on the phase-compensated signal.

[0016] Preferably, the method for summing the Doppler-compensated signals is as follows: sum all Doppler-compensated signals within the same pulse repetition period.

[0017] Preferably, the method for coherently accumulating the summed signal includes: using FFT processing to coherently accumulate the echo signals of the synthesized multiple pulses.

[0018] The advantages of this application include: when the frequency difference between transmitted signals is greater than the bandwidth, this application achieves narrowband coherent processing through phase compensation and Doppler compensation. By increasing the frequency difference between transmitted signals, the transmitted signals are received by different channels of the interceptor, reducing the energy of the radar transmitted signal received by a single channel. Furthermore, based on traditional MIMO radar signal processing, phase difference compensation and Doppler compensation due to the different frequencies of the transmitted signals are added to achieve target detection. Attached Figure Description

[0019] Figure 1 This is a flowchart of a preferred embodiment of the broadband transmission narrowband coherent processing method of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0021] The technical solution of this invention is a narrowband coherent processing method for centralized MIMO radar transmit signals with different frequencies and large frequency differences. Its implementation flowchart is as follows: Figure 1 As shown, firstly, based on each center frequency of the MIMO radar transmitted signal, the received signals from the entire array are down-converted; the down-converted signals are then subjected to matched filtering; given the known position and velocity of the target at the previous moment, multiple ranges and velocities are selected within a certain range and velocity range, and for each range and velocity, the corresponding phase difference and Doppler are calculated, followed by phase compensation and Doppler compensation; the compensated signals are summed; the synthesized signal is then subjected to CFAR detection and the signal-to-noise ratio is calculated; finally, the range and velocity of the target with the highest signal-to-noise ratio among all detected targets are selected.

[0022] The specific steps of the broadband transmit narrowband coherent processing method based on centralized MIMO proposed in this application are as follows:

[0023] The MIMO radar is in tracking mode, with the frequency interval between transmitted signals much larger than the signal bandwidth. The target's position at the previous moment is known. Where R0 is the distance to the target, and θ is the azimuth angle of the target. Let v be the target's elevation angle and velocity be v0. There are M transmitting subarrays, and the center frequencies of the transmitted signals are f1 to f2. M The entire array receives signals, with a total of N receiving array elements, and the number of pulses processed coherently is N. FFT .

[0024] 1. Down-convert the full array received signal based on the center frequency of the MIMO radar transmit signal:

[0025] The echo signals of multiple pulses received by each array element are respectively processed using frequencies f1 to f2. M The local oscillator signal is down-converted to obtain M×N×N FFTIf the signal is a path signal, then the echo signal of the k-th pulse received by the n-th receiving array element, after down-conversion using the m-th local oscillator signal, is expressed as:

[0026]

[0027] Where β is the complex amplitude of the echo signal. T p The pulse width of the signal. It is the reference delay of the target echo. f is the echo delay difference between the m-th transmitting subarray and the n-th receiving element. d,m =2v0 / λ m λ is the Doppler frequency of the target. m =c / f m Let T be the wavelength of the m-th transmitted signal. r The pulse repetition period of the signal is s. m (t) represents the m-th baseband transmitted signal, n n,m,k (t) represents noise.

[0028] 2. Perform matched filtering on the down-converted signal:

[0029] Based on the transmitted baseband signals, the corresponding baseband echo signals of each array element are subjected to matched filtering processing, that is:

[0030] y n,m,k (t)=IFFT{FFT[x n,m,k (t)]·FFT[s m (t)]}

[0031] 3. Select the target distance range and speed range:

[0032] Given the estimated target distance variation range (R0-ΔR1, R0+ΔR2), and selecting multiple distances R1, R2, ... R in small step increments. P Given the predicted target velocity variation range (v0-Δv1, v0+Δv2), and selecting multiple velocities v1, v2, ... v in small step increments. Q By using a traversal method, steps 4 through 8 are repeated for each selected distance and speed.

[0033] 4. Perform phase compensation on the matched-filtered signal:

[0034] Based on the selected distance R i (i = 1, 2, ..., P), θ, The time delay between it and the phase center of each transmitting subarray and each receiving element can be calculated. Based on the calculated time delay and the center frequencies f1 to f2 of each transmitted signal... MPhase compensation is performed on the echo signal, i.e.

[0035]

[0036] 5. Perform Doppler compensation on the phase-compensated signal:

[0037] Based on the selected speed v j Given (j = 1, 2, ..., Q) and the center frequencies of each transmitted signal, calculate the Doppler frequency f. d,j,m =2v j / f m (where j = 1, 2, ... Q, m = 1, 2, ... M), Doppler compensation is performed on the phase-compensated signal, i.e.

[0038] y n,m,k,i,j (t)=y n,m,k,i (t)exp(j2π(f d,j,m -f d,j,1 (k-1)T r )

[0039] 6. Sum the Doppler-compensated signals:

[0040] N is obtained by summing the signals from each channel within the same pulse repetition period. FFT Road signal, i.e.

[0041]

[0042]

[0043] 7. Perform coherent accumulation on the synthesized signal:

[0044] FFT processing was used to process the synthesized N FFT The echo signals of each pulse are coherently accumulated, that is...

[0045] z FFT,i,j (t)=[FFT{z i,j (t)}] T

[0046] 8. Perform CFAR detection on the coherently accumulated signal and calculate the signal-to-noise ratio:

[0047] The CFAR detection method is used to detect targets on the coherently accumulated signal. If a target is detected, its signal-to-noise ratio (SNR) is calculated. i,j .

[0048] 9. Select the CFAR detection result with the highest signal-to-noise ratio as the target's distance and velocity.

[0049] A specific embodiment of the broadband transmit narrowband coherent processing method based on centralized MIMO in this application is as follows:

[0050] S1. Down-convert the full array received signal based on the center frequency of the MIMO radar transmitted signal.

[0051] Parameter settings: The MIMO radar has four transmitting subarrays, each with 99 elements. It uses a full array for receiving, with 396 receiving elements arranged in a triangular grid. The transmitted signal waveform is an LFM signal with center frequencies of f1 = 10 GHz, f1 = 10.04 GHz, f1 = 10.08 GHz, and f1 = 10.12 GHz, a bandwidth of B = 4 MHz, and a pulse width of T. p =10us, pulse repetition period T r =100us, target range, azimuth, and elevation are (7km, 10°, 20°), speed is 50m / s, noise is complex Gaussian white noise with mean of 0 and variance of 1, single-pulse signal-to-noise ratio is -30dB, and the number of coherent pulses is 256. After down-conversion, 405504 signals are obtained.

[0052] S2. Perform matched filtering on the down-converted signal based on the baseband transmitted signal.

[0053] The waveform expression of the baseband transmitted LFM signal is as follows: Among them, pulse width T p =10µs, frequency modulation slope μ = 4 × 10 11 Hz / s

[0054] S3. Select target distance and speed range.

[0055] The estimated target distance ranges from 6.85km to 7.15km, with a distance step size of 37.5m, for a total of 5 distances. The estimated target speed ranges from 30m / s to 70m / s, with a speed step size of 0.5m / s, for a total of 81 speeds. Steps 4-8 are then performed for each selected distance and speed.

[0056] S4. Perform phase compensation on the matched-filtered signal.

[0057] Based on the selected distance, the time delay τ between it and the phase center of each transmitting subarray and each receiving element can be calculated. m,n,i m=1,2,…,4,n=1,2,…,396,i=1,2,…,5, phase compensation is performed on the echo signal based on the calculated time delay and the center frequency of each transmitted signal.

[0058] S5. Perform Doppler compensation on the phase-compensated signal.

[0059] Based on the selected velocity and the center frequency of each transmitted signal, the Doppler frequency f can be calculated. d,j,m j = 1, 2, ..., 81, m = 1, 2, ..., 4, perform Doppler compensation on the phase-compensated signal.

[0060] S6. Summing the Doppler-compensated signals.

[0061] The summation of all Doppler-compensated signals within the same pulse repetition period yields 256 signals.

[0062] S7. Perform coherent accumulation on the synthesized signal.

[0063] FFT processing was used to coherently accumulate the echo signals of the synthesized multiple pulses, with 256 pulses being coherently accumulated.

[0064] S8. Perform CFAR detection on the coherently accumulated signal and calculate the signal-to-noise ratio.

[0065] The CFAR detection method is used to detect targets on the coherently accumulated signal. If a target is detected, its signal-to-noise ratio is calculated.

[0066] S9. Select the CFAR detection result with the highest signal-to-noise ratio as the target's distance and velocity.

[0067] Without phase difference and Doppler compensation caused by different center frequencies, the narrow pulses accumulated near the target range and velocity have two peaks. After compensation using the true target range and velocity, the narrow pulses accumulated at the target range and velocity have only one peak, and the signal-to-noise ratio is improved by approximately 14 dB compared to before compensation.

[0068] This application achieves narrowband coherent processing by using phase compensation and Doppler compensation when the frequency difference between transmitted signals exceeds the bandwidth. By increasing the frequency difference between transmitted signals, the transmitted signals are received by different channels of the interceptor, reducing the energy of the radar transmitted signal received by a single channel. Furthermore, based on traditional MIMO radar signal processing, phase difference compensation and Doppler compensation due to the frequency difference of the transmitted signals are added to achieve target detection.

[0069] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A broadband transmit narrowband coherent processing method based on centralized MIMO, characterized in that: When the MIMO radar is in tracking mode, the frequency interval between transmitted signals is much larger than the signal bandwidth. Step S1: Obtain the target's position and velocity at the previous moment; the position is... ,in Distance to the target The azimuth of the target. Let be the target's pitch angle, and let be the target's velocity. ; Step S2: Based on the target's position and velocity at the previous moment, select multiple position points within a preset range of the position and velocity; give the estimated range of target distance change. And select multiple distances with tiny step sizes. ; Given the range of predicted target velocity changes And select multiple speeds in tiny increments. ; Step S3: Calculate the signal-to-noise ratio of the position and velocity at the plurality of location points; Step S4: Select the CFAR detection result with the highest signal-to-noise ratio as the target's distance and velocity; The method for calculating the signal-to-noise ratio includes: Step S11: Based on the center frequency of the MIMO radar transmission signal, there are M transmission subarrays with transmission signal center frequencies of f1~f M The baseband echo signal is obtained by downconverting the full array received signal. Step S12: Based on each transmitted baseband signal, perform matched filtering on the corresponding baseband echo signal of each array element to obtain the matched filtered signal; Step S13: Perform phase compensation on the matched filter signal, specifically: based on the selected distance , and The time delay between the phase center of each transmitting subarray and each receiving element can be calculated. Based on the calculated time delay and the center frequency of each transmitted signal Phase compensation is performed on the echo signal, i.e. ； Doppler compensation is performed on the phase-compensated signal; specifically, based on the selected velocity... Calculate the Doppler frequency based on the center frequency of each transmitted signal. ,in , Doppler compensation is performed on the phase-compensated signal, i.e. ； T r The pulse repetition period; The Doppler-compensated signals are summed; the summed signals are then coherently accumulated. Step S14: Perform target detection on the coherently accumulated signal; calculate the signal-to-noise ratio of the location points that meet the preset requirements in the detection results.

2. The broadband transmit narrowband coherent processing method based on centralized MIMO as described in claim 1, characterized in that, The method for summing the Doppler-compensated signals is as follows: sum all the Doppler-compensated signals within the same pulse repetition period.

3. The broadband transmit narrowband coherent processing method based on centralized MIMO as described in claim 1, characterized in that, Methods for coherently accumulating the summed signal include: using FFT processing to coherently accumulate the echo signals of the synthesized multiple pulses.

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