阅读说明：本技术 一种基于正交频分信号的雷达解模糊及遮挡的方法 (Radar ambiguity-resolving and shielding method based on orthogonal frequency division signals ) 是由 严济鸿 李聪 董海洋 张欢 翟鉴枢 倪伟涵 杨礼 王顺祥 于 2021-09-15 设计创作，主要内容包括：本发明公开了一种基于正交频分信号的雷达解模糊及遮挡的方法,涉及雷达领域,解决了现有技术中距离模糊和遮挡、速度模糊的问题。本发明包括根据雷达最远探测距离所对应的最大时长和脉冲重复时间间隔PRI,确定在最大探测距离所对应的时间内,采用高重频模式发射正交LFM脉冲信号的个数；对得到的回波矩阵R配合发射脉冲LFM信号进行频域脉冲压缩处理得到处理后的新回波矩阵,并对回波矩阵做MTD处理。本发明同时解决距离遮挡、距离模糊、速度模糊问题。(The invention discloses a radar ambiguity resolution and occlusion method based on orthogonal frequency division signals, relates to the field of radars, and solves the problems of range ambiguity, occlusion and speed ambiguity in the prior art. Determining the number of orthogonal LFM pulse signals transmitted by adopting a high repetition frequency mode within the time corresponding to the maximum detection distance according to the maximum duration corresponding to the farthest detection distance of the radar and the pulse repetition time interval PRI; and carrying out frequency domain pulse compression processing on the obtained echo matrix R in cooperation with the transmitting pulse LFM signal to obtain a new processed echo matrix, and carrying out MTD processing on the echo matrix. The invention simultaneously solves the problems of distance shielding, distance blurring and speed blurring.)

1. A radar ambiguity-resolving and shielding method based on orthogonal frequency division signals is characterized by comprising the following steps:

step 1, determining the time width for transmitting LFM pulse according to the distance blind area and the distance resolution of a radar system;

determining a minimum transmit Pulse Repetition Frequency (PRF) to be used within one radar cycle, based on a maximum radial velocity of the target;

step 2, determining the number of orthogonal LFM pulse signals transmitted by adopting a high repetition frequency mode within the time corresponding to the maximum detection distance according to the maximum duration corresponding to the farthest detection distance of the radar and the pulse repetition time interval PRI;

step 3, transmitting orthogonal LFM pulse signals for multiple times in one radar period CPI to accumulate echo signals detected by a radar system;

and 4, obtaining the echo matrix R constructed in the step 3, performing frequency domain pulse compression processing on the echo matrix R in cooperation with the transmitting pulse LFM signal to obtain a new processed echo matrix, and performing MTD processing on the echo matrix.

2. The method according to claim 1, wherein the orthogonal LFM pulse signal is an orthogonal LFM signal with auto-correlation and cross-correlation properties;

i.e. a for each of the plurality of orthogonal LFM transmit signals₁,a₂,…,a_mThe transmitted signals are orthogonal to each other, and the pulses satisfy

Where E represents the signal energy and m is the number of transmitted signals.

3. The method of claim 2, wherein one radar period CPI in step 3 comprises a time T corresponding to a maximum detection range_maxThe number of the targets is selected in a self-adaptive manner according to the application scene where the targets are located.

4. The method for radar ambiguity resolution and occlusion based on orthogonal frequency division signals as claimed in claim 3, further comprising a preprocessing procedure for the echo signals in step 3, wherein the preprocessing procedure comprises: at T for receiver of radar system_maxDown-converting the internally acquired echo signals to digital baseband signals;

comprising echoes between a plurality of pulses, T_maxPartial nulling of the internal transmit pulse reconstructs a time sequence, which is at T_maxM zero sequences with the same width as the transmitting pulse and m echo sequences are contained.

5. The method according to claim 4, wherein in step 4, the detailed processing method of the frequency domain pulse compression is as follows:

echo R of the first row of the matrix R₁And A is₁Performing frequency domain pulse compression, A₁Is to put 0 after LFM signal a1 of the transmission pulse, and obtain A of equal-length time sequence₁And R₁Substituting into the following formula

X₁＝IFFT(FFT(R₁)·CONJ(FFT(A₁)))

Wherein CONJ is a conjugate operation;

echo R of the second row of the matrix R₂And A is₂Performing frequency domain pulse compression, A₂Is transmitting a pulse LFM signal a₂Is followed by 0 to obtain equal-length time series A₂And R₂；

And performing the above processing on each row of the matrix R, putting the processed data into a corresponding row of the new matrix X, performing FFT (fast Fourier transform) on each column of the new matrix X, namely performing MTD (maximum likelihood decomposition) processing, wherein a peak value in the matrix is used for expressing the distance and the speed of a target.

6. The method according to any one of claims 1-5, wherein the radar system employs a transmit-receive switching mode, and during part of the radar period, the transmitted signal employs another pulse repetition frequency, and the another pulse repetition frequency is slightly greater than the minimum pulse repetition frequency.

Technical Field

The invention relates to the field of radar, in particular to a radar ambiguity resolution and shielding method based on orthogonal frequency division signals.

Background

The digital array radar has many advantages, and has become the mainstream of the radar field at present. In the searching stage of the digital array radar, no prior information exists, the information such as target distance, speed, angle and the like is unknown, in order to detect a target at a longer distance, a Pulse Doppler (PD) radar system is often adopted, a transmitting antenna and a receiving antenna are shared (or the transmitting antenna and the receiving antenna are not shared, the transmitting antenna and the receiving antenna are switched to each other, and the receiving of target echoes by the radar can not be influenced by transmitting leakage.

The radar of the pulse system can generate distance ambiguity when the delay time of a target echo is longer than the repetition period of a transmitted pulse. Velocity ambiguity can occur when the doppler frequency caused by object motion is greater than half the repetition frequency of the transmit pulses.

To solve the speed ambiguity problem, a High Pulse Repetition Frequency (HPRF) operation mode can be used, but also the distance ambiguity and distance occlusion problems are caused. In order to solve the distance ambiguity problem, the conventional method adopts several different Pulse Repetition Intervals (PRI), and the selection of the PRI is usually based on the remainder theorem, the one-dimensional set algorithm, the lookup table method, etc., but the above methods all have respective disadvantages.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the invention provides a radar ambiguity resolution and occlusion method based on orthogonal frequency division signals, which solves the problems.

In the traditional radar signal method, the echo between two pulses is subjected to pulse compression processing, so that the problem of distance ambiguity occurs.

The invention is realized by the following technical scheme:

step 1, determining the time width for transmitting an LFM pulse according to the range blind area and the range resolution of a radar system so as to ensure that a target echo signal cannot be overlapped with a transmitted pulse;

determining a minimum transmit Pulse Repetition Frequency (PRF) to be used within one radar period according to a maximum radial velocity of the target to ensure that velocity ambiguity does not occur;

step 2, determining the number of orthogonal LFM pulse signals transmitted by adopting a high repetition frequency mode in the time corresponding to the maximum detection distance according to the maximum duration corresponding to the farthest detection distance of the radar and the pulse repetition time interval PRI, wherein the high repetition frequency mode is adopted to avoid the speed ambiguity of the radar;

the orthogonal LFM pulse signal is an orthogonal LFM signal with self-correlation and cross-correlation performances;

i.e. a for each of the plurality of orthogonal LFM transmit signals₁,a₂,…,a_mThe transmitted signals are orthogonal to each other, and the pulses satisfy

Wherein E represents signal energy;

wherein, the reciprocal of the repetition frequency PRF of the transmitted pulse, PRI is the time interval of two adjacent transmitted pulses, and the time T corresponding to the maximum detection distance is determined_maxThe number of LFM pulse signals (i.e. m pulse signals a) which are orthogonal to each other₁,a₂,…,a_m) The LFM pulse signals are orthogonal pairwise, and have good autocorrelation and cross-correlation performance (namely, autocorrelation side lobes and cross-correlation side lobes are low);

step 3, transmitting orthogonal LFM pulse signals for multiple times in one radar period CPI to accumulate echo signals detected by a radar system;

further, one radar period CPI in step 3 includes a time T corresponding to the maximum detection distance_maxAccording to the application of the targetAnd carrying out self-adaptive selection on the scene.

In step 3, a preprocessing process of the echo signal is further included, wherein the preprocessing process comprises the following steps: at T for receiver of radar system_maxDown-converting the internally acquired echo signals to digital baseband signals;

comprising echoes between a plurality of pulses, T_maxPartial nulling of the internal transmit pulse reconstructs a time sequence, which is at T_maxM zero sequences with the same width as the transmitting pulse and m echo sequences are contained.

In the matrix R constructed by the method, the first row time length is T_max(with a)₁The signal transmission starting time is the time length after the starting), the second line time length is also T_max(with a)₂The time when the signal starts to be transmitted is the time length after the signal starts to be transmitted), and so on in subsequent rows.

If more than one T is included in a radar period CPI_maxThe same process is performed for subsequent echoes in a CPI to obtain an echo matrix R, as shown below.

In step 4, obtaining the echo matrix R constructed in the step 3, performing frequency domain pulse compression processing on the echo matrix R in cooperation with the transmitting pulse LFM signal to obtain a processed new echo matrix, and performing MTD processing on the echo matrix;

the detailed processing method of the frequency domain pulse compression comprises the following steps:

echo R of the first row of the matrix R₁And A is₁Performing frequency domain pulse compression, A₁Is to put 0 after LFM signal a1 of the transmission pulse, and obtain A of equal-length time sequence₁And R₁Substituting into the following formula

X₁＝IFFT(FFT(R₁)·CONJ(FFT(A₁)))

Wherein CONJ is a conjugate operation;

echo R of the second row of the matrix R₂And A is₂For pulsing in frequency domainCompression, A₂Is transmitting a pulse LFM signal a₂Is followed by 0 to obtain equal-length time series A₂And R₂；

And performing the above processing on each row of the matrix R, putting the processed data into a corresponding row of the new matrix X, performing FFT (fast Fourier transform) on each column of the new matrix X, namely performing MTD (maximum likelihood decomposition) processing, wherein a peak value in the matrix is used for expressing the distance and the speed of a target.

In a traditional PD radar, echoes of different pulses to different range targets may overlap, and the peak value of the MTD result of the traditional method is range-blurred and is not enough to distinguish different targets from the overlapping echoes. After the processing, even if the echo is the superposition of a plurality of target echoes, the peak value in the MTD result can show that different targets are positioned at different distances, thus solving the distance fuzzy problem of echo superposition.

The radar adopts a receiving and transmitting switching mode, so that the problem of distance shielding is inevitably generated. In order to avoid the distance obstruction caused by the transceiving switching, in some radar periods, the transmitting signal can adopt another pulse repetition frequency which is slightly larger than the minimum pulse repetition frequency, and the orthogonal LFM pulse signal (as b in the figure) is adopted₁,b₂,…,b_nThe orthogonal LFM signals are pairwise orthogonal, have good autocorrelation and cross-correlation performance, and n is slightly larger than m). The distance shielding problem is solved through the emission of two different pulse repetition frequencies and the subsequent radar signal processing.

The invention has the following advantages and beneficial effects:

the invention simultaneously solves the problems of distance shielding, distance blurring and speed blurring.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

fig. 1 is a schematic diagram of the orthogonal LFM pulse signal transmitted in one radar cycle according to the present invention.

Fig. 2 is a diagram of MTD of a conventional PD radar transmitting the same LFM pulse signal.

Fig. 3 is a diagram of the MTD of the present invention transmitting orthogonal LFM pulse signals.

Detailed Description

Hereinafter, the term "comprising" or "may include" used in various embodiments of the present invention indicates the presence of the invented function, operation or element, and does not limit the addition of one or more functions, operations or elements. Furthermore, as used in various embodiments of the present invention, the terms "comprises," "comprising," "includes," "including," "has," "having" and their derivatives are intended to mean that the specified features, numbers, steps, operations, elements, components, or combinations of the foregoing, are only meant to indicate that a particular feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as first excluding the existence of, or adding to the possibility of, one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing.

In various embodiments of the invention, the expression "or" at least one of a or/and B "includes any or all combinations of the words listed simultaneously. For example, the expression "a or B" or "at least one of a or/and B" may include a, may include B, or may include both a and B.

Expressions (such as "first", "second", and the like) used in various embodiments of the present invention may modify various constituent elements in various embodiments, but may not limit the respective constituent elements. For example, the above description does not limit the order and/or importance of the elements described. The foregoing description is for the purpose of distinguishing one element from another. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of various embodiments of the present invention.

It should be noted that: if it is described that one constituent element is "connected" to another constituent element, the first constituent element may be directly connected to the second constituent element, and a third constituent element may be "connected" between the first constituent element and the second constituent element. In contrast, when one constituent element is "directly connected" to another constituent element, it is understood that there is no third constituent element between the first constituent element and the second constituent element.

The terminology used in the various embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the various embodiments of the invention. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments of the present invention belong. The terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning that is consistent with their contextual meaning in the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein in various embodiments of the present invention.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

Linear Frequency Modulation (LFM) signals are widely used pulse pressure radar signals, and the invention aims to reduce the working blind area of an LFM pulse radar and reduce the width of a transmitted pulse, namely the length of a code sheet of the LFM signal, as much as possible; in order to solve the problem of speed ambiguity, a High Pulse Repetition Frequency (HPRF) working mode is adopted, and the problem of distance ambiguity can be solved by adopting the received signal processing method, namely a frequency domain pulse compression method;

the specific embodiment is as follows:

the sampling rate of the PD radar receiver is 100MHz, the bandwidth B of a single LFM pulse signal is 10MHz (the frequencies of 4 LFM pulse signals are 0-10MHz, 10-20MHz, 20-30MHz and 30-40MHz respectively), the pulse width tau is 1.28 mu s, the pulse repetition Period (PRI) is 64 mu s, and one radar period T is_maxThe phase-coherent integration period (CPI) includes 4 PRIs and 16 Ts_maxThe radio frequency f is 3GHz and c isThe speed of light. The distance resolution at this time is

Distance from the blind area

Maximum unambiguous distance of

Maximum unambiguous velocity of

The distance of the target is set to 20km, the speed of the target is 270m/s, and the signal-to-noise ratio is set to-15 dB. If the same signal is used for the transmitted signals, the MTD result is shown in fig. 2, and it is not possible to distinguish which echo is the echo of which transmitted pulse signal, resulting in range ambiguity.

By adopting the method disclosed by the patent, the LFM pulse signals which are orthogonal to each other are transmitted, the MTD result is shown in figure 3, the distance and the speed of the target can be accurately measured, and the figure only has one peak value, namely, the problem of distance ambiguity does not exist.

In order to avoid the distance shielding caused by the receiving and transmitting switching (the target echo of the current transmitting pulse signal is delayed and overlapped with a certain transmitting pulse, the echo signal is not received and processed, and the target information can not be obtained), the embodiment adopts another pulse repetition frequency, and one radar period T_maxIt contains 5 PRIs. The distance shielding problem of the PD radar can be solved by transmitting two different pulse repetition frequencies and processing subsequent radar signals.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.