阅读说明：本技术 一种近距离复杂多径环境下毫米波雷达实时测距方法 (Millimeter wave radar real-time ranging method under short-distance complex multipath environment ) 是由 李拴劳 张爱军 牛文博 王振西 贾建超 王路阳 韩东娟 于 2021-07-23 设计创作，主要内容包括：一种近距离复杂多径环境下毫米波雷达实时测距方法,对传统的CFAR检测方法进行了改进,针对近距离复杂环境下的多径回波信号,在选取参考单元时避免取到多径信号,进而避免了由此带来的信噪比下降乃至漏警,提出的判断是否检测到多径信号及多径信号剔除的方法运算量小,可靠性高,易于硬件的实时处理,满足深空探测的轻小型化、高可靠的设计要求。(A millimeter wave radar real-time ranging method under a short-distance complex multipath environment is improved, a traditional CFAR detection method is improved, multipath signals are prevented from being acquired when a reference unit is selected for multipath echo signals under the short-distance complex environment, further, signal to noise ratio reduction and even false alarm caused by the multipath signals are avoided, the method for judging whether the multipath signals are detected or not and eliminating the multipath signals is small in operation amount and high in reliability, hardware real-time processing is easy, and light, small and high-reliability design requirements of deep space detection are met.)

1. A millimeter wave radar real-time ranging method under a short-distance complex multipath environment is characterized by comprising the following steps:

(1) performing coherent accumulation on each pulse echo to obtain an accumulated one-dimensional range profile;

(2) performing CFAR detection on the accumulated one-dimensional range profile;

(3) carrying out continuity judgment on the detected target; if the judgment result has the multipath signal, entering the step (4), otherwise entering the step (5);

(4) removing the multipath signals, and entering the step (5);

(5) obtaining the beam center of the target without the multipath signal;

(6) and calculating the real-time distance of the millimeter wave radar according to the design parameters of the radar system and the position of the distance unit corresponding to the beam center.

2. The millimeter wave radar real-time ranging method in the short-distance complex multipath environment as recited in claim 1, wherein:

in the step (1), all pulse echoes of the same distance unit to be detected are subjected to azimuth FFT, the obtained mode maximum value is taken as the echo of the distance unit, all pulses of each distance unit to be detected are processed to obtain an accumulated one-dimensional range profile, an echo signal is x [ n ] [ m ], and the determination method of the accumulated one-dimensional range profile is as follows:

in the formula, FFT is fast Fourier transform, Sigma is summation operation, max is maximum operation, abs is modulo operation, y is one-dimensional distance image after accumulation, m is distance unit number, y is echo signal after processing.

3. The millimeter wave radar real-time ranging method in the short-distance complex multipath environment as recited in claim 2, wherein:

in the step (2), the specific steps for performing CFAR detection are as follows:

and according to the distance corresponding to the distance unit to be detected, taking the echo area of the distance unit as a protection unit, not selecting a reference unit in the echo area of the distance unit, taking the distance unit corresponding to the secondary multipath, the tertiary multipath, the echo broadening and the side lobe of the distance unit as the protection unit, not selecting the protection unit as the reference unit, and performing CFAR detection according to the one-dimensional distance image of the distance unit to be detected to determine the position of the target.

4. The millimeter wave radar real-time ranging method in the short-distance complex multipath environment as recited in claim 3, wherein:

in the step (3), the continuity judgment specifically comprises:

further detecting the detected target, if the number of the distance units in the target is less than the number of the distance units between the front edge and the rear edge of the detected target, the target has multipath signals and needs to be subjected to multipath removal processing; otherwise, no multi-path signal exists, and the step (5) is entered.

5. The millimeter wave radar real-time ranging method in the short-distance complex multipath environment as recited in claim 4, wherein:

in the step (4), the specific steps of multipath signal elimination are as follows:

and processing the distance unit corresponding to the detected target by taking the distance zero point as a reference, and removing the distance unit and the targets detected thereafter as multipath signals when the distance corresponding to the detected target is more than 1.5 times of the distance corresponding to the front edge of the detected target without counting the calculation of the beam center.

6. The millimeter wave radar real-time ranging method in the short-distance complex multipath environment as recited in claim 5, wherein:

in the step (5), the specific method for obtaining the beam center Y includes:

in the formula, k_minFor the nearest distance unit of the detected object, k_maxIs the farthest distance unit without multipath signal, e is the distance unit value corresponding to the detected target, y [ e ]]The amplitude value is the amplitude value on the one-dimensional range profile corresponding to the range unit.

7. The millimeter wave radar real-time ranging method in the short-distance complex multipath environment as recited in claim 6, wherein:

in the step (6), the method for calculating the real-time distance of the millimeter wave radar comprises the following steps:

calculating the distance R at the moment according to the center Y of the obtained target beam, specifically as follows:

wherein B is the radar transmission signal bandwidth, T_PFor transmitting signal time width, f_sAnd N is the FFT point number of the baseband signal after digital down-conversion.

Technical Field

The invention relates to a millimeter wave radar real-time distance measurement method in a close-range complex multipath environment, and belongs to the field of space microwave remote sensing.

Background

In the landing detection of extraterrestrial celestial bodies such as moon, mars, asteroid and the like, a microwave distance and speed measuring sensor is key equipment of a navigation, guidance and control (GNC) subsystem of a lander, and provides distance and speed information of the lander relative to the surface of the extraterrestrial celestial body for the GNC subsystem in real time in the landing process, so that the landing precision and safety are ensured, and whether the lander can land to a specified detection area with high precision and high reliability is determined. The microwave distance and speed measuring sensor is the name of a detector for microwave distance and speed measuring equipment, namely a commonly understood microwave distance and speed measuring radar, and the current working frequency band reaches the Ka wave band. The high frequency band ensures high-precision distance and speed measurement, but the high frequency band is more sensitive to the environment, especially the requirement of future deep space exploration tasks on the nearest acting distance of a microwave distance and speed measuring sensor is higher and higher, even the nearest acting distance is required to be less than 1m, at the moment, radar echoes are coupled with multiple path signals which are reflected to the surface of an extraterrestrial celestial body through a bottom plate of a lander and then return, and the multipath signals can be detected by directly detecting a target according to a traditional radar detection method, so that distance and speed measurement errors are caused. Therefore, an effective, highly reliable, highly precise real-time distance measuring method in engineering is urgently needed, which can be adapted to the complex multipath environment in a short distance.

Disclosure of Invention

The technical problem solved by the invention is as follows: aiming at the problem that in the prior art, multipath signals can be detected by directly detecting targets according to a traditional radar detection method, so that distance and speed measurement errors are caused, the millimeter wave radar real-time ranging method under the short-distance complex multipath environment is provided.

The technical scheme for solving the technical problems is as follows:

a millimeter wave radar real-time ranging method under a short-distance complex multipath environment comprises the following steps:

(1) performing coherent accumulation on each pulse echo to obtain an accumulated one-dimensional range profile;

(2) performing CFAR detection on the accumulated one-dimensional range profile;

(3) carrying out continuity judgment on the detected target; if the judgment result has the multipath signal, entering the step (4), otherwise entering the step (5);

(4) removing the multipath signals, and entering the step (5);

(5) obtaining the beam center of the target without the multipath signal;

(6) and calculating the real-time distance of the millimeter wave radar according to the design parameters of the radar system and the position of the distance unit corresponding to the beam center.

In the step (1), all pulse echoes of the same distance unit to be detected are subjected to azimuth FFT, the obtained mode maximum value is taken as the echo of the distance unit, all pulses of each distance unit to be detected are processed to obtain an accumulated one-dimensional range profile, an echo signal is x [ n ] [ m ], and the determination method of the accumulated one-dimensional range profile is as follows:

in the formula, FFT is fast Fourier transform, Sigma is summation operation, max is maximum operation, abs is modulo operation, y is one-dimensional distance image after accumulation, m is distance unit number, y is echo signal after processing.

In the step (2), the specific steps for performing CFAR detection are as follows:

and according to the distance corresponding to the distance unit to be detected, taking the echo area of the distance unit as a protection unit, not selecting a reference unit in the echo area of the distance unit, taking the distance unit corresponding to the secondary multipath, the tertiary multipath, the echo broadening and the side lobe of the distance unit as the protection unit, not selecting the protection unit as the reference unit, and performing CFAR detection according to the one-dimensional distance image of the distance unit to be detected to determine the position of the target.

In the step (3), the continuity judgment specifically comprises:

further detecting the detected target, if the number of the distance units in the target is less than the number of the distance units between the front edge and the rear edge of the detected target, the target has multipath signals and needs to be subjected to multipath removal processing; otherwise, no multi-path signal exists, and the step (5) is entered.

In the step (4), the specific steps of multipath signal elimination are as follows:

and processing the distance unit corresponding to the detected target by taking the distance zero point as a reference, and removing the distance unit and the targets detected thereafter as multipath signals when the distance corresponding to the detected target is more than 1.5 times of the distance corresponding to the front edge of the detected target without counting the calculation of the beam center.

In the step (5), the specific method for obtaining the beam center Y includes:

in the formula, k_minFor the nearest distance unit of the detected object, k_maxIs the farthest distance unit without multipath signal, e is the distance unit value corresponding to the detected target, y [ e ]]The amplitude value is the amplitude value on the one-dimensional range profile corresponding to the range unit.

In the step (6), the method for calculating the real-time distance of the millimeter wave radar comprises the following steps:

calculating the distance R at the moment according to the center Y of the obtained target beam, specifically as follows:

wherein B is the radar transmission signal bandwidth, T_PFor transmitting signal time width, f_sAnd N is the FFT point number of the baseband signal after digital down-conversion.

Compared with the prior art, the invention has the advantages that:

the millimeter wave radar real-time distance measurement method under the short-distance complex multipath environment provided by the invention improves the traditional CFAR detection method, avoids obtaining multipath signals when selecting a reference unit aiming at multipath echo signals under the short-distance complex environment, further avoids signal to noise ratio reduction and even false alarm caused by the multipath signals, has small operand and high reliability, is easy for real-time processing of hardware, meets the light, small and high-reliability design requirements of deep space detection, can effectively remove the multipath signals and obtain correct distance values by measurement, has small computation amount, and can meet the requirements of hardware resources and real-time property.

Drawings

FIG. 1 is a flow chart of data processing provided by the present invention;

FIG. 2 is a schematic diagram of the coherent integration provided by the present invention;

FIG. 3 is a schematic diagram of reference unit selection during CFAR detection provided by the present invention;

FIG. 4 is a schematic diagram of the target continuity determination provided by the present invention;

FIG. 5 is a schematic diagram of multi-path signal rejection provided by the present invention;

Detailed Description

A millimeter wave radar real-time ranging method under a short-distance complex multipath environment is provided, aiming at the multipath problem caused by the complex environment existing when a microwave ranging and speed measuring sensor works in a short distance, a method for distinguishing and eliminating multipath signals is provided, the interference of the multipath signals can be effectively eliminated, the real-time ranging is realized with high reliability and high precision, and the specific steps of the ranging method are as follows:

(1) performing coherent accumulation on each pulse echo to obtain an accumulated one-dimensional range profile;

the method comprises the following steps of carrying out azimuth FFT on all pulse echoes of the same distance unit to be detected, taking the obtained maximum value of a module as the echo of the distance unit, processing all pulses of each distance unit to be detected, and then obtaining an accumulated one-dimensional distance image, wherein an echo signal is x [ n ] [ m ], and the method for determining the accumulated one-dimensional distance image comprises the following steps:

in the formula, FFT is fast Fourier transform, Sigma is summation operation, max is maximum operation, abs is modulo operation, ym is one-dimensional distance image after accumulation, m is distance unit number, yn is echo signal after processing;

(2) performing CFAR detection on the accumulated one-dimensional range profile;

the specific steps for CFAR detection are as follows:

taking the echo area of the range unit as a protection unit according to the distance corresponding to the range unit to be detected, not selecting a reference unit in the echo area of the range unit, taking the secondary multipath, the tertiary multipath, the echo broadening and the range unit corresponding to the side lobe of the range unit as the protection unit, not selecting the protection unit as the reference unit, and performing CFAR detection according to the one-dimensional range profile of the range unit to be detected to determine the position of a target;

(3) carrying out continuity judgment on the detected target; if the judgment result has the multipath signal, entering the step (4), otherwise entering the step (5);

wherein, the continuity judgment is specifically as follows:

further detecting the detected target, if the number of the distance units in the target is less than the number of the distance units between the front edge and the rear edge of the detected target, the target has multipath signals and needs to be subjected to multipath removal processing; otherwise, no multi-path signal exists, and the step (5) is carried out;

(4) removing the multipath signals, and entering the step (5);

the method for eliminating the multipath signals comprises the following specific steps:

processing a distance unit corresponding to the detected target by taking the distance zero point as a reference, and taking the distance unit and the targets detected thereafter as multipath signals to remove without calculating the center of a beam when the distance corresponding to the detected target is more than 1.5 times of the distance corresponding to the front edge of the detected target;

(5) obtaining the beam center of the target without the multipath signal;

the specific method for solving the beam center Y is as follows:

in the formula, k_minFor the nearest distance unit of the detected object, k_maxIs the farthest distance unit without multipath signal, e is the distance unit value corresponding to the detected target, y [ e ]]The amplitude value on the one-dimensional range profile corresponding to the range unit;

(6) calculating the real-time distance of the millimeter wave radar according to the design parameters of the radar system and the position of the distance unit corresponding to the center of the calculated wave beam, wherein:

the method for calculating the real-time distance of the millimeter wave radar comprises the following steps:

calculating the distance R at the moment according to the center Y of the obtained target beam, specifically as follows:

wherein B is the radar transmission signal bandwidth, T_PFor transmitting signal time width, f_sAnd N is the FFT point number of the baseband signal after digital down-conversion.

The following is further illustrated with reference to specific examples:

in the current embodiment, as shown in fig. 1, which is a flowchart of a millimeter wave radar real-time ranging method in a short-distance complex multipath environment, in the first step, echoes of a plurality of pulses are subjected to coherent accumulation to obtain an accumulated one-dimensional range profile; secondly, performing CFAR detection on the accumulated one-dimensional range profile; thirdly, carrying out continuity judgment on the detected target; fourthly, when the existence of the multipath signals is judged, the multipath signals are removed; fifthly, solving the beam center of the target from which the multipath signals are removed; and sixth step row distance calculation. The invention relates to a millimeter wave radar real-time ranging method under a short-distance complex multipath environment, which comprises the following specific steps:

pulse coherent integration

As shown in fig. 2, in order to achieve a high signal-to-noise ratio, a radar generally transmits a plurality of pulses, and performs coherent accumulation on echoes of the plurality of pulses to improve the signal-to-noise ratio. The specific process is to perform azimuth FFT on all pulse echoes of the same range cell, then take the modulo maximum value as the echo of the range cell, and perform the above processing on all range cells to obtain the accumulated one-dimensional range image, as shown in fig. 2. Let the echo signal be x [ n ] [ m ], and its calculation method is:

wherein, FFT represents fast Fourier transform, Sigma [ ] represents summation operation, max [ ] represents maximum operation, abs [ ] represents modulus operation, y [ m ] represents one-dimensional distance image after accumulation, and m is distance unit number.

Second, CFAR detection

As shown in fig. 3, after obtaining the one-dimensional range image of the target, target detection is required to determine the target position. The invention provides an improved CFAR detection method, which can solve the problem that the traditional CFAR detection can possibly obtain multipath signals when the reference unit is taken when the multipath signals exist, thereby further causing the signal-to-noise ratio to be greatly reduced and even causing alarm leakage. The improved CFAR detection protection unit and the reference unit are selected according to the following principle: according to the distance corresponding to the distance unit to be detected, the broadening and the side lobe of the echo of the distance unit to be detected are considered, the area needs to be used as a protection unit, and a reference unit cannot be selected in the area; meanwhile, the secondary multipath, the tertiary multipath, the echo broadening and the distance unit corresponding to the side lobe of the distance unit are used as protection units and cannot be selected as reference units. FIG. 3 is a schematic diagram of a reference cell selection.

Third, target continuity judgment

As shown in fig. 4, the continuity determination of the detected target refers to a determination method based on the continuity of the target, which is proposed to identify whether the detected target includes a multipath signal. The criterion is as follows: if the number of the detected target distance units is less than the number of the detected distance units between the front edge and the rear edge of the target, the existence of multipath signals is considered, and multipath removal processing is required; otherwise, the multi-path signal is not detected, and the beam center is directly obtained. As shown in the left diagram of fig. 4, the distance unit corresponding to the detected leading edge of the target is k₁The distance unit corresponding to the target trailing edge is k₂The number of detected target units is k₂-k₁+1, so the detected object is continuous at this time, no multipath signal is detected; in the right diagram of FIG. 4, the number of detected targets is k₂-k₁+k₄-k₃+2, the front and back edges of the detected target are k respectively₁、k₄So that the corresponding number of target range cells is k₄-k₁+1, obviously k₂-k₁+k₄-k₃+2<k₄-k₁+1, so it can be determined that the multipath signal is detected at this time, and the multipath signal elimination process is needed.

Four, multi-path signal rejection

As shown in fig. 5, when the detected target has a multipath signal, the following elimination processing is performed: and judging a distance unit corresponding to the detected target by taking the distance zero point as a reference, and if the distance corresponding to the detected target is more than 1.5 times of the distance corresponding to the front edge of the detected target, taking the distance unit and the target detected later as multipath signals to remove, and not participating in calculation when calculating the beam center. As shown in fig. 5, the objects detected by the shaded portions are eliminated.

Fifthly, obtaining the center of the wave beam

In order to improve the ranging accuracy, the center of the wave beam of the echo is obtained by adopting a gravity center method, and the specific method comprises the following steps: assuming that the most of the targets are detectedShort distance unit is k_minThe farthest distance unit is: k is a radical of_max(after multipath removal), the beam center is the center of gravity corresponding to the section of the object detected on the one-dimensional range profile, which can be expressed as:

wherein e represents the distance unit value corresponding to the detected target, and y [ e ] is the amplitude value on the one-dimensional distance image corresponding to the distance unit.

Sixthly, distance calculation

And calculating to obtain a distance value according to the design parameters of the radar system and the required distance unit position corresponding to the beam center. Assuming that the bandwidth of a radar transmission signal is B and the time width of the transmission signal is T_PThe signal sampling rate after deskew is f_sIf the number of FFT points of the baseband signal after the digital down-conversion is N, the distance R at the moment can be calculated according to the calculated target beam center Y:

after the processing of the steps, the real-time ranging under the short-distance complex multipath environment can be realized.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.

Those skilled in the art will appreciate that the details of the invention not described in detail in this specification are well within the skill of those in the art.