Wideband Radar Single-Bit Data Transmission and Sparse Imaging Method

Abstract

The present invention discloses a method for single-bit data transmission and sparse imaging of broadband radar, belonging to the technical field of radar imaging, which includes the following steps: Step S1, convert the broadband radar echo and the threshold into binary data with the same number of bits through data conversion; Step S2, process according to the positive or negative nature of the threshold; Step S3, according to the order of sampling points, arrange the extracted bits to form a decimation method; Step S4, decimate one bit of data from the broadband radar echo in the order of sampling points according to the decimation method in Step S3, and arrange the extracted one-bit data according to the sampling point data to form single-bit echo data, that is, realize variable-threshold single-bit quantization; Step S5, use the single-bit radar two-dimensional sparse imaging algorithm for imaging. By adopting the above method for single-bit data transmission and sparse imaging of broadband radar, the present invention can not only reduce the hardware overhead, relieve the transmission and storage pressure of the broadband radar system, but also ensure the imaging quality.

Description

Technical Field

[0001] The present invention relates to the technical field of radar imaging, and in particular to a method for broadband radar single-bit data transmission and sparse imaging. Background Art

[0002] Currently, synthetic aperture radar (SAR) has become an indispensable electronic equipment due to its all-weather and all-time imaging capabilities. When applied, SAR is usually required to have high resolution in order to obtain detailed information of the target scene. High-precision imaging depends on high-bit sampling quantization, high sampling rate, and large-scale data processing. However, the massive echo data will bring heavy burdens on data acquisition, storage, transmission, and processing, significantly increasing the system complexity and cost. Single-bit radar imaging technology can effectively alleviate this problem, not only reducing the pressure on data storage and transmission, but also lowering the system cost, so it has important research value in both military and civilian fields.

[0003] At present, the single-bit radar hardware system has not yet developed to a mature stage. To achieve the single-bit quantization effect, usually the sign bit of the broadband radar echo is directly extracted to generate single-bit echo data. However, this method will cause the complete loss of the amplitude information of the scatterers, thus affecting the effective recognition of the target and the imaging quality. Research shows that by applying a variable threshold to the broadband radar echo and then extracting the sign bit, the amplitude information of the scatterers can be restored to a certain extent. However, implementing the variable threshold requires additional hardware resources to generate the dynamic threshold signal.

[0004] If a Gaussian threshold is used, its random characteristics not only significantly increase the hardware burden, but also the threshold information is difficult to reproduce, affecting the operability and stability. In contrast, a single-frequency threshold only requires three key parameters: amplitude, frequency, and phase, to generate a determinable single-frequency signal, thus avoiding the reproduction problem caused by randomness. However, in the dechirp receiving acquisition system, the broadband radar echo is affected by the single-frequency threshold, and a significant spectral line will be introduced in the range domain, thus reducing the imaging quality. In addition, the single-frequency threshold still relies on additional hardware resources to generate and maintain, thus increasing the hardware burden of the system and being unfavorable for the efficient deployment of small platforms.

[0005] In recent years, the research on small-platform broadband radar systems has been continuously heating up and has become one of the focus points in the field of broadband radar technology. With the wide application of unmanned aerial vehicles, portable broadband radar devices, and embedded systems, the demand for low-power, lightweight, and high-performance broadband radar solutions is increasing day by day. However, limited by the computing power, storage resources, and energy consumption budget of small platforms, how to achieve high-quality radar imaging under limited hardware conditions has become the key challenge in current research. Summary of the Invention

[0006] The object of the present invention is to provide a wideband radar single-bit data transmission back and sparse imaging method, which can not only reduce the hardware cost, relieve the transmission and storage pressure of the wideband radar system, but also achieve single-frequency threshold single-bit quantization of the wideband radar echo data, effectively restore the target scattering intensity information, and ensure the imaging quality.

[0007] To achieve the above object, the present invention provides a wideband radar single-bit data transmission back and sparse imaging method, including the following steps:

[0008] Step S1: Convert the wideband radar echo and the threshold into binary data with the same number of bits through data conversion;

[0009] Step S2: Process according to the positive or negative nature of the threshold;

[0010] When the threshold is positive, extract the number of bits of the highest non-zero bit in the threshold binary data;

[0011] When the threshold is negative, extract the number of bits of the highest zero bit in the threshold binary data;

[0012] Step S3: According to the order of the sampling points, arrange the extracted number of bits to form a decimation method;

[0013] Step S4: Decimate one bit of the radar echo in the order of the sampling points according to the decimation method in Step S3, and arrange the extracted one-bit data in the order of the sampling point data to form single-bit echo data, that is, realize variable-threshold single-bit quantization;

[0014] Step S5: Use a single-bit radar two-dimensional sparse imaging algorithm for imaging.

[0015] Preferably, in Step S1, set the wideband radar to transmit a linear frequency modulation signal, the number of pulses transmitted by the wideband radar is N , the number of sampling points of each pulse is M , that is, the radar imaging scene is grid points, and the wideband radar echo is expressed as:

[0016] ;

[0017] Among them, is the fast time; is the slow time; and are the scattering coefficient and distance of the th sampling point in the th pulse; is the pulse width; is the frequency modulation rate; is the carrier frequency; is the speed of light; is the reference distance; is the imaginary unit; is the unit rectangular function, , ;

[0018] .

[0019] Preferably, the wideband radar echo is written in matrix form , expressed as:

[0020] ;

[0021] wherein, , the th element of is ; , the th element of is ; , the th element of is:

[0022] ;

[0023] wherein, is the width of the imaging scene in the range direction; is the distance of the th grid point in the width of the imaging scene in the range direction, ; is the th moment; , the th element of is , is the th Doppler frequency; is expressed as the slow time at the th moment; is the Doppler frequency, , , , .

[0024] Preferably, noise is added to the matrix form of the wideband radar echo , , and it is written in the real matrix form expressed as:

[0025] ;

[0026] Among them, the specific expressions of each item are as follows:

[0027] .

[0028] Preferably, in step S1, the threshold signal is represented by a Fourier series, including a single-frequency threshold, a sawtooth threshold, and a triangular threshold. Its general expression is:

[0029] ;

[0030] Among them, is the coefficient of the Fourier series, is the frequency of the signal.

[0031] Preferably, when generating a single-frequency signal in the form of a negative complex number, the coefficient of its Fourier series is expressed as:

[0032] ;

[0033] Among them, is the amplitude of the single-frequency signal. Then the specific expression of the single-frequency threshold is:

[0034] .

[0035] Preferably, when generating a sawtooth signal, the coefficient of the Fourier series is:

[0036] ;

[0037] When generating a sawtooth threshold of a real signal, the specific expression of the sawtooth threshold is:

[0038] .

[0039] Preferably, when generating a triangular signal, the coefficient of the Fourier series is:

[0040] ;

[0041] When generating a triangular threshold in the form of a real number, the specific expression of the triangular threshold is:

[0042] ;

[0043] Among them, is an odd number.

[0044] Furthermore, set the threshold amplitude information.

[0045] The amplitude of the threshold needs to be determined according to the signal threshold ratio Set it to ensure the amplitude information of the effective recovery signal, and the signal threshold ratio The specific expression is:

[0046] ;

[0047] Among them, is the amplitude of the echo signal. When , the amplitude of the signal after single-bit quantization , , has a linear relationship, that is:

[0048] ;

[0049] In order to better maintain the integrity of the signal amplitude information, usually is required to have a good effect of recovering the signal amplitude information. Then The expression is:

[0050] .

[0051] Preferably, the single-bit echo data obtained in step S4 is expressed as:

[0052] ;

[0053] Among them, represents the loop operation of steps S1 - S4 on the data. The single-bit echo data is written in matrix form , and is expressed as:

[0054] ;

[0055] That is, .

[0056] Preferably, in step S5, the probability density function of is derived under the condition of , and the probability density function of is derived. The objective function is obtained according to the maximum a posteriori probability, and the objective function is simplified; specifically:

[0057] Set the noise to follow an independent and identically distributed Gaussian random variable with a mean of 0 and a variance of , and obtain the probability density function of under the condition of :

[0058] ;

[0059] in, for No. elements, for No. OK, for No. List, , ; , z 、 t is the variable of the function;

[0060] Set Vector Elements Obey the independent and identically distributed Laplace distribution, then The probability density function of for:

[0061] ;

[0062] in, is the scale factor, for No. elements; for No. elements; the objective function is obtained according to the maximum a posteriori probability formula, and the objective function is simplified to:

[0063] .

[0064] Therefore, the present invention adopts the above-mentioned broadband radar single-bit data return and sparse imaging method, and the technical effects are as follows:

[0065] (1) The present invention proposes a variable threshold extraction method and uses this method to extract one bit of data from the broadband radar echo, and uses this one bit of data as single-bit echo data, thereby realizing variable threshold single-bit quantization, avoiding the use of additional circuits, and significantly reducing hardware overhead.

[0066] (2) The present invention proposes a method for extracting radar echoes to obtain one bit of data, converting high-precision radar echo data into single-bit radar echo data, which can reduce the transmission and storage pressure of broadband radar systems;

[0067] (3) The present invention proposes a variable threshold extraction method that can effectively restore the scattering intensity information of the scattering point, thereby improving the imaging quality;

[0068] (4) The present invention proposes a single-bit radar two-dimensional sparse reconstruction algorithm, which effectively avoids the problem that the reconstruction accuracy in one dimension of one-dimensional sparse reconstruction is not high, resulting in a decrease in the reconstruction accuracy in the second dimension, and realizes fine imaging of the single-bit radar.

[0069] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 is a flowchart of an embodiment of the method for backhauling single-bit data and sparse imaging of a broadband radar according to the present invention;

[0071] Figure 2 is the result of two-dimensional sparse imaging of a high-precision radar;

[0072] Figure 3 is the result of two-dimensional sparse imaging of a single-bit radar with a zero threshold;

[0073] Figure 4 is the result of two-dimensional sparse imaging of a single-bit radar with a single-frequency threshold;

[0074] Figure 5 is the result of two-dimensional sparse imaging of a single-bit radar based on single-frequency extraction;

[0075] Figure 6 is the result of two-dimensional sparse imaging of a single-bit radar based on sawtooth extraction;

[0076] Figure 7 is the result of two-dimensional sparse imaging of a single-bit radar based on triangular extraction. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0077] The technical solution of the present invention will be further described below with reference to the drawings and embodiments.

[0078] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0079] Embodiment 1

[0080] As Figure 1 shown, the present invention provides a method for backhauling single-bit data and sparse imaging of a broadband radar, including the following steps:

[0081] Step S1, converting the broadband radar echo and the threshold into binary data with the same number of bits through data conversion to ensure the consistency of calculation. Set the broadband radar to transmit a linear frequency modulation signal, and the number of pulses transmitted by the broadband radar is N Each pulse has M sampling points, that is, the radar imaging scene is grid points, and the broadband radar echo Expressed as:

[0082] ;

[0083] in, For fast time; For slow time; and For the In the pulse Scattering coefficient and distance of each sampling point; is the pulse width; To adjust the frequency; is the carrier frequency; is the speed of light; is the reference distance; is an imaginary unit; is the unit rectangle function, , ;

[0084] ;

[0085] Broadband radar echo Written in matrix form , expressed as:

[0086] ;

[0087] in, , No. The elements are ; , No. The elements are ; , No. The elements are:

[0088] ;

[0089] in, is the width of the imaging scene in the range direction; The width of the imaging scene in the distance direction The distance between grid points, ; for No. a moment; , No. The elements are , For the Doppler frequency; Denoted as the slow time at the moment; is the Doppler frequency, , , , .

[0090] Adding noise to the wideband radar echo in matrix form, , , written in the form of a real number matrix is expressed as:

[0091] ;

[0092] where the specific expressions of each term are:

[0093] .

[0094] Among them, the threshold signal is represented by Fourier series, including single-frequency threshold, sawtooth threshold, and triangular threshold, and its general expression is:

[0095] ;

[0096] where, are the coefficients of the Fourier series, is the frequency of the signal;

[0097] When generating a single-frequency signal in negative complex form, the coefficients of its Fourier series are expressed as:

[0098] ;

[0099] where, is the amplitude of the single-frequency signal, then the specific expression of the single-frequency threshold is:

[0100] ;

[0101] The coefficients of the Fourier series of the sawtooth wave signal are:

[0102] ;

[0103] When generating a sawtooth threshold of a real signal, the specific expression of the sawtooth threshold is:

[0104] ;

[0105] When generating a triangular signal, the coefficients of the Fourier series are:

[0106] ;

[0107] When generating a triangular threshold in real number form, the specific expression of the triangular threshold is:

[0108] ;

[0109] where is an odd number.

[0110] Set the threshold amplitude information.

[0111] The amplitude of the threshold needs to be set according to the signal threshold ratio to ensure the effective recovery of the amplitude information of the signal. The specific expression of the signal threshold ratio is:

[0112] ;

[0113] where is the amplitude of the echo signal. When , the amplitude , , after single-bit quantization of the signal has a linear relationship, that is:

[0114] ;

[0115] In order to better maintain the integrity of the signal amplitude information, usually is required to have a good effect of recovering the signal amplitude information. Then the expression of is:

[0116] .

[0117] Step S2: Process according to the positive or negative nature of the threshold;

[0118] When the threshold is positive, extract the number of bits of the highest non-zero bit in the threshold binary data; for example: the threshold signal is represented by a 16-bit signed binary as , and the number of bits corresponding to the highest non-zero bit is 12, that is, the number of bits corresponding to in the data;

[0119] When the threshold is negative, extract the number of bits of the highest zero bit in the threshold binary data; for example: the threshold signal is represented by a 16-bit signed binary as , and the number of bits corresponding to the highest non-zero bit is 11, that is, the number of bits corresponding to in the data;

[0120] Step S3: Arrange the extracted number of bits according to the order of the sampling points to form a decimation method;

[0121] Step S4: Extract one bit of data from the broadband radar echo in the order of sampling points according to the extraction method in Step S3, and arrange the extracted one-bit data in the order of sampling point data to form single-bit echo data, that is, realize variable-threshold single-bit quantization. The single-bit echo data obtained in Step S4 is expressed as:

[0122] ;

[0123] wherein, represents the loop operation of Steps S1 - S4 on the data, and the single-bit echo data Y is written in matrix form as:

[0124] ;

[0125] that is, .

[0126] Step S5: Use the single-bit radar two-dimensional sparse imaging algorithm for imaging, specifically, derive the probability density function of under the condition of , and derive the probability density function of , obtain the objective function according to the maximum a posteriori probability, and simplify the objective function; specifically:

[0127] Set the noise to follow an independent and identically distributed Gaussian random variable with a mean of 0 and a variance of , and obtain the probability density function of under the condition of :

[0128] ;

[0129] wherein, is the th element of , is the th row of , is the th column of , , ; , z , t are the variables of the function;

[0130] Set the elements of the vector to follow an independent and identically distributed Laplace distribution, then the probability density function of is is:

[0131] ;

[0132] wherein, is a scale factor, is the th element of; is the th element of; The objective function is obtained according to the maximum a posteriori probability formula, and the objective function is simplified to:

[0133] .

[0134] The effect of the present invention is further illustrated by the results of simulation experiments. The software used in the simulation experiments is MATLAB.

[0135] The specific simulation experiment is as follows:

[0136] The experimental conditions for simulating aircraft point targets are: carrier frequency 10 GHz, pulse repetition frequency 400 Hz, bandwidth 400 MHz, pulse width , sampling rate 4 MHz, coherent processing interval , target rotation speed , signal-to-noise ratio 15 dB.

[0137] As Figure 2 shown, it is the two-dimensional sparse imaging result of a high-precision radar. Since the two-dimensional sparse reconstruction algorithm can obtain the target scattering intensity information more accurately using high-precision data, therefore, the experimental result is used as a control group in the present invention to illustrate the effectiveness of other algorithms.

[0138] As Figure 3 shown, it is the two-dimensional sparse imaging result of a zero-threshold single-bit radar. It can be seen from the figure that since single-bit quantization is non-linear quantization, the target scattering intensity information is lost, and due to the harmonic and intermodulation components brought by single-bit quantization, the imaging quality is degraded.

[0139] As Figure 4 shown, it is the two-dimensional sparse imaging result of a single-frequency threshold single-bit radar. Since a variable threshold is introduced during single-bit quantization, this algorithm can effectively recover the target scattering intensity. However, since the radar is in a de-chirp receiving mode, introducing a single-frequency threshold will cause a spectral line in the range direction, resulting in a degradation of the imaging quality.

[0140] As Figure 5 , Figure 6 , Figure 7As shown, they are the two-dimensional sparse imaging results of single-bit radar based on single-frequency extraction, sawtooth extraction, and triangular extraction respectively. It can be seen that this method can not only recover the target scattering intensity information, but also there will be no single spectral line in the range direction, thus improving the imaging quality.

[0141] Therefore, by adopting the above-mentioned method for backhauling single-bit data and sparse imaging of wideband radar, the present invention can not only reduce the hardware cost, relieve the transmission and storage pressure of the wideband radar system, but also achieve single-frequency threshold single-bit quantization of the wideband radar echo data, effectively recover the target scattering intensity information, and ensure the imaging quality.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A broadband radar single-bit data transmission back and sparse imaging method, characterized in that It includes the following steps: Step S1: Convert the broadband radar echo and the threshold into binary data with the same number of bits through data conversion; Step S2: Process according to the positive or negative nature of the threshold; When the threshold is positive, extract the number of bits of the highest non-zero bit in the threshold binary data; When the threshold is negative, extract the number of bits of the highest zero bit in the threshold binary data; Step S3: According to the order of the sampling points, arrange the extracted number of bits to form a decimation method; Step S4: Decimate one bit of the broadband radar echo in the order of the sampling points according to the decimation method in Step S3, and arrange the extracted one-bit data in the order of the sampling point data to form single-bit echo data, that is, realize variable-threshold single-bit quantization; Step S5: Use the single-bit radar two-dimensional sparse imaging algorithm for imaging.

2. The broadband radar single-bit data backhaul and sparse imaging method according to claim 1, characterized in that In step S1, a broadband radar is set to transmit a linear frequency modulation signal, and the number of pulses transmitted by the broadband radar is N , and the number of sampling points for each pulse is M , that is, the broadband radar imaging scene is grid points, and the broadband radar echo is expressed as: ； wherein, is the fast time; is the slow time; and are the scattering coefficient and distance of the th sampling point within the th pulse; is the pulse width; is the frequency modulation rate; is the carrier frequency; is the speed of light; is the reference distance; is the imaginary unit; is the unit rectangular function, , ; .

3. The broadband radar single-bit data feedback and sparse imaging method according to claim 2, wherein Write the broadband radar echo in matrix form , which is expressed as: ； Among them, , the th element of ; , the th element of ; , the th element of: ； in, is the width of the imaging scene in the range direction; The width of the imaging scene in the distance direction The distance between grid points, ; for No. a moment; , No. The elements are , For the Doppler frequencies; Expressed as The slow time of the moment, ; is the Doppler frequency, , , .

4. The broadband radar single-bit data transmission and sparse imaging method according to claim 3, characterized in that In the broadband radar echo Add noise to the matrix form , , and write it in the form of a real number matrix It is expressed as: ； Among them, the specific expressions of each item are: 。 5. The broadband radar single-bit data transmission back and sparse imaging method according to claim 4, wherein In Step S1, the threshold signal is represented by a Fourier series, including a single-frequency threshold, a sawtooth threshold, and a triangular threshold, and its general expression is: ； Among them, is the coefficient of the Fourier series, is the frequency of the signal.

6. The broadband radar single-bit data transmission and sparse imaging method according to claim 5, wherein When generating a single-frequency signal in the form of a negative complex number, the coefficients of its Fourier series are expressed as: ； Among them, is the amplitude of the single-frequency signal, and the specific expression of the single-frequency threshold is: 。 7. The broadband radar single-bit data feedback and sparse imaging method according to claim 5, wherein When generating a sawtooth wave signal, the coefficients of the Fourier series are: ； When generating a sawtooth threshold of a real signal, the specific expression of the sawtooth threshold is: 。 8. The broadband radar single-bit data feedback and sparse imaging method according to claim 5, wherein When generating a triangular signal, the coefficients of the Fourier series are: ； When generating a triangular threshold in the form of a real number, the specific expression of the triangular threshold is: ； Among them, is an odd number.

9. The broadband radar single-bit data backhaul and sparse imaging method according to claim 4, wherein The single-bit echo data obtained in step S4 is expressed as: ； Among them, represents performing a loop operation on the data in steps S1 - S4, and writing the single-bit echo data in matrix form , which is expressed as: ； That is, .

10. The broadband radar single-bit data backhaul and sparse imaging method according to claim 9, characterized in that In step S5, derive the probability density function under the condition of and the probability density function of . According to the maximum a posteriori probability, obtain the objective function and simplify the objective function, specifically as follows: ​ Set noise Gaussian random variables that are independent and identically distributed, with a mean of 0 and a variance of , obtaining Under the condition of The probability density function of : ； Among them, is the th element of is the th row of is the th column of , ; , , are variables of the function; Set vector elements of follow independent and identically distributed Laplace distributions, then probability density function of is: ； Among them, is the scale factor, is the th element of; is the th element of; Obtain the objective function according to the maximum a posteriori probability formula, and simplify the objective function to get: 。

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