CN107783122B - Fixed wing unmanned aerial vehicle collision avoidance system radar signal processing apparatus based on millimeter wave radar - Google Patents
Fixed wing unmanned aerial vehicle collision avoidance system radar signal processing apparatus based on millimeter wave radar Download PDFInfo
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- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
Fixed wing unmanned aerial vehicle collision avoidance system radar signal processing apparatus based on millimeter wave radar belongs to the signal processing field, and in order to solve the fixed wing unmanned aerial vehicle collision avoidance system radar signal processing problem of millimeter wave radar, the technical essential includes: the acquisition module is used for AD data acquisition; the direct current removing module is used for removing direct current; the window function processing module is used for processing the window function; the FFT conversion module is used for FFT conversion; the threshold detection module is used for CFAR threshold detection; the binary detection module is used for binary detection; the pairing processing module is used for pairing processing; and the resolving module is used for resolving speed and/or distance and/or angle. The device can realize the detection of the relative distance and the relative speed of the front obstacle and can realize the detection function of the target direction angle.
Description
Technical Field
The invention belongs to the field of signal processing, and relates to a radar signal processing device.
Background
The unmanned aerial vehicle is an unmanned aerial vehicle and is an unmanned aerial vehicle operated by utilizing a radio remote control device and a self-contained program control device. According to the application field, the method can be divided into military use and civil use. The civil field of unmanned aerial vehicles can be further subdivided into two main categories: one is administrative departments, such as meteorology, police, surveying and mapping, environmental protection, scientific research, disaster prevention and management, and the like; one is commercial, such as film and television aerial photography, agriculture and forestry plant protection, electric power energy routing inspection and the like. At present, unmanned aerial vehicles in China are widely applied in government departments, and are also rapidly popularized in the commercial field.
The american consumer electronics association data shows that 40 million worldwide civilian drones are expected to sell in 2015, and the market size is expected to increase 55% over the last year, reaching $ 1.3 billion. By 2018, market demand will soon emerge, with the expectation that the global drone market will scale to at least $ 10 billion.
Although the civil unmanned aerial vehicle is not large in scale in the current domestic market, the civil unmanned aerial vehicle is wide in application and huge in future development space. The domestic civil unmanned aerial vehicle is demanded to be 0.5 hundred million dollars in 2013, the domestic civil unmanned aerial vehicle is expected to keep the speed increase of more than 20% in the next 10 years, and the market scale of the domestic unmanned aerial vehicle is expected to approach 3 hundred million dollars in 2022.
Unmanned aerial vehicle mainly divide into rotor unmanned aerial vehicle and fixed wing unmanned aerial vehicle. The two unmanned aerial vehicles have different flying principles, so that the two unmanned aerial vehicles respectively have different characteristics. Many rotor unmanned aerial vehicle relies on the lift that a plurality of rotors produced to come the gravity of balanced aircraft, lets the aircraft can fly, controls the steady and the gesture of aircraft through the rotational speed that changes every rotor. Therefore, the multi-rotor aircraft can hover and fly at any speed within a certain speed range, basically is an aerial flying platform, can be additionally provided with sensors, cameras and the like, even instruments such as manipulators and the like, is simple to operate, and can be operated by people through simple training. At present, unmanned aerial vehicle rotor companies mainly include companies such as Dajiang and parrot.
The fixed-wing unmanned aerial vehicle takes thrust generated by a propeller or a turbine engine as power for forward flight of the aircraft, and the main lifting force is from relative movement of wings and air. Therefore, fixed wing aircraft must have a certain airless relative velocity to fly with lift. Because of the principle, the fixed wing aircraft has the characteristics of high flying speed, economy and high carrying capacity. Fixed wing drones are also very useful, and are generally selected when large voyage and altitude demands are met, such as power line patrol, highway monitoring and the like.
Fixed wing aircraft have both advantages and disadvantages when compared to rotorcraft. Fixed wing aircraft are more forgiving in the face of piloting and technical errors in the air due to their natural ability to glide when they are without power. Fixed wing aircraft also have the ability to fly to greater distances with greater loads at low battery. Fixed wing aircraft are at a disadvantage when precise missions are required. As they must have air flowing over their wings to generate lift. This means that they must remain moving forward, that is they cannot hover in a location like an aircraft and therefore cannot provide an accurate level of camera position. Therefore, for longer and more heavily loaded tasks, a fixed wing is the best choice.
Unmanned aerial vehicles have been developed for many years, and how to let unmanned aerial vehicles perceive distance and avoid obstacles is a great problem all the time. Foreign relevant organizations count that 10 accidents happen to helicopters on average in every 10000h of flight, and among various accidents, the accident rate caused by collision with obstacles in low-altitude flight accounts for about 35%, and far exceeds other accident reasons. The object threatening the outdoor low-altitude flight safety of the unmanned aerial vehicle mainly comprises natural objects such as trees and the like and artificial objects such as power lines, telegraph poles and buildings, wherein the power lines are small in size and difficult to find by naked eyes, so that the flying safety hazard to the unmanned aerial vehicle is the greatest.
The earliest distance measurement method is actually somewhat like a reversing radar, emits electric waves to a distance measurement object through the hearing similar to bats, senses the direction and the position of an object after reflection. An AR.Drone unmanned aerial vehicle under the Parrot flag of French unmanned aerial vehicle company firstly measures distance to the lower part in an ultrasonic mode, so that the unmanned aerial vehicle can fly at the same height; the second generation (XIRO X plorer 2) of the seeker of the zero-degree unmanned aerial vehicle adopts a special infrared mode to measure 360-degree distance, thereby avoiding the obstacle. However, the maximum limitations of radar ranging are: it needs to transmit electric wave first and then reconnaissance electric wave reflection; under the limit of endurance and radio wave emission power, it is difficult to perform long-distance ranging: for example, the ultrasound height of the Parrot Bebop Drone is set to be 8 meters at the maximum distance, and the maximum avoidance radius of the zero degree seeker 2 is 6 meters. Xinntom 4 or Yuneec Typhoon H in Xinjiang penetrates through the binocular sensor, and as long as the automatic obstacle avoidance distance is far longer than that of an ultrasonic radar type obstacle avoidance under a good light environment: the binocular sensor in Da Jiang can judge the obstacle about 15 meters farthest, which is nearly one time farther than the Parrot Bebop Drone. However, the obstacle avoidance is realized by adopting vision, and the obstacle avoidance function is greatly influenced by environmental changes.
According to the technical method, the visual sensor, the infrared sensor and the ultrasonic radar sensor are mainly used for avoiding obstacles in the flight environment of the unmanned aerial vehicle, but due to the fact that the sensors are close in action distance, obstacle avoidance response time is short in the process of fast flight of the fixed-wing unmanned aerial vehicle, and the fixed-wing unmanned aerial vehicle is susceptible to severe weather and sudden environmental changes, and therefore obstacle avoidance failure and the like are caused.
Disclosure of Invention
In order to solve the problem of radar signal processing of a fixed-wing unmanned aerial vehicle collision avoidance system of a millimeter wave radar, the technical scheme of the invention is as follows:
the utility model provides a fixed wing unmanned aerial vehicle collision avoidance system radar signal processing apparatus based on millimeter wave radar, includes:
the acquisition module is used for AD data acquisition;
the direct current removing module is used for removing direct current;
the window function processing module is used for processing the window function;
the FFT conversion module is used for FFT conversion;
the threshold detection module is used for CFAR threshold detection;
the binary detection module is used for binary detection;
the pairing processing module is used for pairing processing;
and the resolving module is used for resolving speed and/or distance and/or angle.
Has the advantages that: the invention provides a millimeter wave radar-based radar signal processing device of a fixed-wing unmanned aerial vehicle collision avoidance system, which can detect the relative distance and relative speed of a front obstacle and can also realize the detection function of a target direction angle. Due to the adoption of more signal processing methods, the anti-collision system can output more stable target information, and can perform more accurate detection on the obstacle target for the fixed-wing unmanned aerial vehicle.
Drawings
FIG. 1 is a graph of the frequency variation of a chirped triangular wave FMCW over a frequency sweep period;
figure 2 rotor unmanned aerial vehicle short distance collision avoidance system signal processing flow chart.
Detailed Description
Example 1: a radar signal processing method of a fixed-wing unmanned aerial vehicle collision avoidance system based on a millimeter wave radar comprises the following steps:
s1, AD data acquisition;
s2, removing direct current;
s3, processing a window function;
s4, FFT conversion;
s5, CFAR threshold detection;
s6, binary detection;
s7, pairing;
and S8, resolving the speed and/or the distance and/or the angle.
As an example, in step S1:
(1) carrying out digital processing on the continuous IQ data in the channel 1 and the channel 2 through AD sampling;
(2) dividing the data collected in the channel 1 and the channel 2 into upper frequency sweep data and lower frequency sweep data of triangular waves, removing front part data points, namely removing the front part data points collected by AD in the data collected by AD, generally removing the front part data points collected by AD at 50-70 points, for example, if 700 points are collected, removing the front 50 points, and performing direct current conversion on the data from 51 to 700 and performing FFT conversion. The partial point to be removed has two reasons, namely, the data is the abnormal partial data caused by the pulse generated by the voltage when the waveform is changed, and the second reason is the distance ambiguity. This part is not the reason for the reduction in range resolution as described above, but rather the linearity of the transmitted waveform, which causes this reduction in resolution.
As an example, in step S2:
(1) respectively calculating the mean values of upper and lower sweep IQ data of the channel triangular wave in the channel 1 and the channel 2;
(2) and subtracting the mean value obtained by the previous step of calculation from each data of the upper and lower sweep IQs of the triangular wave of each channel, thereby finishing the purpose of removing direct current and reducing the influence of a direct current part on the detection of a target threshold.
In step S3, windowing the time domain data after the respective dc removal of the upper and lower sweep frequency segments of the triangular wave in the channel 1 and the channel 2, and selecting a hanning window and/or a hamming window to reduce side lobes, thereby improving the detection performance of the target; the hanning window will cause the main lobe to widen and decrease, but the side lobes will decrease significantly. The Hamming window and the Hanning window are cosine windows, and only have different weighting coefficients. The coefficient of the hamming window weighting enables the side lobes to be smaller.
As an example, in step S5:
(1) averaging the complex modulus of each point after the sweep frequency FFT conversion on the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion on the triangular wave in the channel 2, and averaging the complex modulus of each point after the sweep frequency FFT conversion under the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion under the triangular wave in the channel 2;
(2) and carrying out CFAR threshold detection on the averaged data. The CFAR threshold detection can select a threshold detection method SO-CFAR with an average selected unit, the protection unit can select 1 to 2 points, and the number of window points can select 15 to 20.
In the step S6: and for the data after CFAR threshold detection, making each data be a distance unit, namely a distance gate 1 to a distance gate n, wherein n is the number of points of FFT conversion, and performing binary detection on the data of each distance unit, namely recording the data of each distance unit as 1 if the data of the distance unit passes a threshold, and recording the data of each distance unit as 0 if the data of the distance unit does not pass the threshold. And then performing multi-period accumulation, if the number of threshold accumulation 1 of a certain distance unit exceeds K, outputting the coordinate value of the point, otherwise, outputting the coordinate value as a target which passes a threshold, wherein: k represents the number of 1 s accumulated. This can improve the probability of detection of the target.
After binary detection, when the number of points meeting the requirement of passing the threshold is not unique, only the first peak point of the output threshold is selected, and the object which has the largest danger degree to the unmanned plane and is closest to the unmanned plane is mainly considered, so that the maximum peak points of all the thresholds are not found, but the peak value of the first threshold is selected.
As an example, in step S7: after CFAR detection and binary detection, pairing the points passing through the threshold of the upper frequency sweep and the lower frequency sweep, and if the difference of the coordinate values of the points passing through the threshold of the upper frequency sweep and the lower frequency sweep exceeds the threshold, not determining the upper frequency sweep and the lower frequency sweep of the same target, and not performing pairing. As a scheme, the threshold is set to be 25 points or more different from the coordinate values of the points where the upper and lower frequency sweeps pass the threshold.
Calculating the corresponding frequency value of the matched peak point, and setting the peak coordinate of the first threshold point of the up-scan frequency band in the channel 1 as p1_ up, wherein the corresponding frequency value is f1_ up, the corresponding FFT-transformed data is a _ p1_ up +1j b _ p1_ up, and the phase is
The FFT transformed data of the point corresponding to the upper scanning frequency band in the channel 2 is a _ p2_ up +1j b _ p2_ up, and the phase is
Setting the peak value coordinate of the first threshold passing point of the lower sweep frequency segment in the channel 1 as p1_ down, and setting the frequency value corresponding to the point as f1_ down; wherein: a represents the data value of the I path, b represents the data value of the Q path, a _ p1_ up represents that in the array formed by a + j b, the corresponding coordinate of the peak value point of the threshold crossing is p1_ up, b _ p1_ up represents that in the array formed by a + j b, the corresponding coordinate of the peak value point of the threshold crossing is p1_ up.
As an example, in step S8, the distance calculation method is: obtaining the frequency value f1_ up of the upper sweep frequency in the channel 1 and the frequency value f1_ down corresponding to the lower sweep frequency according to a formula
Obtaining the distance of the unmanned aerial vehicle to the obstacle target, wherein T is a triangular wave period, T is 20ms, B is a bandwidth, B is 200MHz, c is the speed of light, and c is 3.0 × 108；
The speed calculation method comprises the following steps: obtaining the frequency value f1_ up of the upper sweep frequency in the channel 1 and the frequency value f1_ down corresponding to the lower sweep frequency according to a formula
Obtaining the speed of the unmanned plane forward obstacle target, wherein f0Is the center frequency, f0＝24.125GHz；
The angle calculation method comprises the following steps: in channel 1 and channel 2, the phases are respectively calculated according to the respective upper frequency sweeps
And
according to a calculation formula
Obtaining the phase difference delta psi;
according to the formula
And calculating the azimuth angle, wherein lambda is the wavelength, and d is the antenna spacing.
Example 2: as a supplement to the technical solution of embodiment 1, this embodiment patent realizes the fixed wing unmanned aerial vehicle and keeps away the barrier function through adopting millimeter wave radar sensor. Because millimeter wave radar operating wavelength is between 1mm ~ 10mm, compare with other detection methods, it is stable mainly to have a detection performance, environmental adaptation is good, and the size is little, the price is low, can be in advantages such as the sleet weather use of abominable relatively, and millimeter wave radar's operating range is far away, to in the fixed wing unmanned aerial vehicle system, for can accurately obtaining fixed wing unmanned aerial vehicle flight place ahead barrier target distance, resolving of speed and azimuth, this embodiment has designed a fixed wing unmanned aerial vehicle collision avoidance system radar signal processing method based on millimeter wave radar.
This embodiment is accomplished rotor unmanned aerial vehicle and is measured its flight place ahead environmental barrier's distance, speed and azimuth mainly. The front obstacles are mainly aimed at people, trees, walls, nets, high-voltage lines and other targets.
The millimeter wave radar designed by the embodiment has the working frequency of 24GHz or 77GHz, adopts an FMCW continuous wave system, and adopts linear frequency modulation, so that the distance resolution is high. The waveform adopts a chirp triangular wave FMCW, mainly because the calculation of the target distance and speed is realized by the present embodiment. Target distance and speed calculation can be achieved through the upper frequency sweep and the lower frequency sweep of the triangular wave. The maximum flying speed of the fixed-wing unmanned aerial vehicle designed by the embodiment is 120km/h, and the maximum distance measurement of unmanned aerial vehicle collision avoidance is 120 m.
The embodiment mainly provides the design of a fixed wing unmanned aerial vehicle anti-collision signal processing part based on the millimeter wave radar and a signal processing method.
The radar center frequency f designed by the embodiment is 24.125 GHz. Triangular waves are selected as the emission waveforms, the period is 20ms, and the bandwidth is 200 MHz. The transmit waveform is shown in fig. 1.
In the embodiment, the resolving of the target distance and speed is realized through single-path IQ data, and because the calculation of the target azimuth angle is realized in the embodiment, the embodiment adopts a double-receiving antenna mode, namely, two-path IQ data, and the angle measurement function of the target is realized through the calculation of respective up-scanning frequency bands of two paths.
Fig. 2 shows a processing flow chart of the anti-collision millimeter wave radar signal of the fixed-wing unmanned aerial vehicle, which specifically comprises the following implementation steps:
1.AD data acquisition, i.e. data processing
(1) Carrying out digital processing on the continuous IQ data in the channel 1 and the channel 2 through AD sampling;
(2) dividing the data collected in the channel 1 and the channel 2 into upper sweep frequency data and lower sweep frequency data of triangular waves, and respectively selecting the data with good linearity for subsequent processing;
2. remove direct current
(1) Respectively calculating the mean values of upper and lower sweep IQ data of the channel triangular wave in the channel 1 and the channel 2;
(2) and subtracting the mean value obtained by the previous step of calculation from each data of the upper and lower sweep IQs of the triangular wave of each channel, thereby finishing the purpose of removing direct current and reducing the influence of a direct current part on the detection of a target threshold.
3. Window function processing
Windowing the time domain data after respectively removing direct current from the upper and lower sweep frequency sections of the triangular wave in the channel 1 and the channel 2, wherein a Hanning window, a Hamming window and the like can be selected to reduce side lobes, so that the detection performance of the target is improved; the hanning window will cause the main lobe to widen and decrease, but the side lobes will decrease significantly. The Hamming window and the Hanning window are cosine windows, and only have different weighting coefficients. The coefficient of the hamming window weighting enables the side lobes to be smaller.
4.FFT transformation
And performing FFT (fast Fourier transform) on the data of the upper and lower frequency sweeping sections of the windowed triangular wave in the channel 1 and the channel 2, and converting time domain data into frequency data.
5.CFAR threshold detection
(1) Averaging the complex modulus of each point after the sweep frequency FFT conversion on the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion on the triangular wave in the channel 2, and averaging the complex modulus of each point after the sweep frequency FFT conversion under the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion under the triangular wave in the channel 2 in the same way;
(2) and carrying out CFAR threshold detection on the averaged data. The CFAR threshold detection can select a threshold detection method SO-CFAR with an average selected unit, the protection unit can select 1 to 2 points, and the number of window points can select 15 to 20.
6. Binary detection
For the data after CFAR threshold detection, each data is made to be a distance unit, i.e. a distance gate 1 to a distance gate n, where n is the number of points of FFT. The data of each distance unit is binary detected, namely, if the data of the distance unit exceeds a threshold, the data is recorded as 1, and if the data of the distance unit does not exceed the threshold, the data of the distance unit is recorded as 0. And then, performing multi-period accumulation, if the number of threshold accumulation 1 of a certain distance unit exceeds K, outputting the coordinate value of the point, and otherwise, outputting the point as a target which passes through the threshold. This can improve the probability of detection of the target.
(3) After binary detection, when the number of points which meet the requirement of threshold crossing is large, only the first peak point which outputs the threshold crossing is selected, mainly considering that the object which has the largest danger degree to the unmanned plane and is closest to the unmanned plane is considered, so the maximum peak points of all the threshold crossing are not found, but the peak value of the first threshold crossing is selected.
7. Pairing process
And matching the points of the upper sweep frequency and the lower sweep frequency which pass the threshold through CFAR detection and binary detection. And if the difference of the coordinate values of the point of which the upper frequency sweep and the lower frequency sweep pass the threshold is too large, the upper frequency sweep and the lower frequency sweep of the same target cannot be determined, and the pairing processing is not carried out.
8. Speed, distance solution
(1) Calculating a frequency value corresponding to the peak point after successful pairing, and setting the peak coordinate of the first threshold point of the up-scan frequency band in the channel 1 as p1_ up, wherein the frequency value corresponding to the peak point is f1_ up, the corresponding FFT data is a _ p1_ up +1j _ b _ p1_ up, the phase is a _ p2_ up +1j b _ p2_ up, and the FFT data of the point corresponding to the up-scan frequency band in the channel 2 is a _ p2_ up +1j _ b _ p2_ up; setting the peak value coordinate of the first threshold passing point of the lower sweep frequency segment in the channel 1 as p1_ down, and setting the frequency value corresponding to the point as f1_ down;
(2) according to a formula, an upper sweep frequency value f1_ up and a frequency value f1_ down corresponding to a lower sweep frequency in the channel 1 obtained in the third step are calculated, wherein T is a triangular wave period, T is 20ms, B is a frequency modulation bandwidth, B is 200MHz, and c is the speed of light; according to the formula, where is the center frequency, 24.125 GHz. According to the two formulas, the distance and the speed of the unmanned aerial vehicle forward obstacle target are obtained;
9. angle resolution
In the channel 1 and the channel 2, the phase sum is respectively calculated according to the respective upper sweep frequency, and the phase difference is calculated according to a calculation formula.
And calculating the azimuth angle according to a formula, wherein d is the antenna spacing.
So far, accomplish single detection and accomplish the function of resolving of rotor unmanned aerial vehicle anticollision millimeter wave radar to information such as unmanned aerial vehicle operation place ahead barrier distance, speed and azimuth.
10. In order to improve the accuracy of resolving the distance, speed and angle information of the target, a multi-period data sliding window processing mode is adopted, namely IQ data acquired by AD of each channel in multiple periods are subjected to average processing. The accuracy of the detected target can be effectively improved by adopting a multi-cycle sliding window type processing method. The selection of the number of the cycles of the sliding window is mainly based on the premise that the target is within the cycles and no cross-unit condition occurs, and then the principle that the chip processing capacity can reach real-time performance is considered.
The design description of the radar signal processing method of the fixed-wing unmanned aerial vehicle collision avoidance system based on the millimeter wave radar is provided above.
Example 3: the utility model provides a fixed wing unmanned aerial vehicle collision avoidance system radar signal processing apparatus based on millimeter wave radar, includes:
the acquisition module is used for AD data acquisition;
the direct current removing module is used for removing direct current;
the window function processing module is used for processing the window function;
the FFT conversion module is used for FFT conversion;
the threshold detection module is used for CFAR threshold detection;
the binary detection module is used for binary detection;
the pairing processing module is used for pairing processing;
and the resolving module is used for resolving speed and/or distance and/or angle.
The acquisition module:
(1) carrying out digital processing on the continuous IQ data in the channel 1 and the channel 2 through AD sampling;
(2) and dividing the data collected in the channel 1 and the channel 2 into upper sweep frequency data and lower sweep frequency data of triangular waves, and removing front part of data points.
The direct current removing module:
(1) respectively calculating the mean values of upper and lower sweep IQ data of the channel triangular wave in the channel 1 and the channel 2;
(2) and subtracting the mean value obtained by the previous step of calculation from each data of the upper and lower sweep IQs of the triangular wave of each channel.
And the window function processing module is used for windowing the time domain data after the upper and lower frequency sweep sections of the triangular wave respectively remove direct current in the channel 1 and the channel 2, and selecting a Hanning window and/or a Hamming window.
The threshold detection module:
(1) averaging the complex modulus of each point after the sweep frequency FFT conversion on the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion on the triangular wave in the channel 2, and averaging the complex modulus of each point after the sweep frequency FFT conversion under the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion under the triangular wave in the channel 2;
(2) and carrying out CFAR threshold detection on the averaged data.
The binary detection module:
and for the data after the CFAR threshold detection, making each data be a distance unit, performing binary detection on the data of each distance unit, then performing multi-period accumulation, if the number of threshold accumulation 1 of a certain distance unit exceeds K, outputting the coordinate value of the point, otherwise, outputting the coordinate value as a target which passes through the threshold, wherein: k represents the number of 1 s accumulated.
After binary detection, when the number of the points which simultaneously meet the requirement of the threshold is not unique, only the first peak point which outputs the threshold is selected.
The pairing processing module: after CFAR detection and binary detection, pairing the points passing through the threshold of the upper frequency sweep and the lower frequency sweep, and if the difference of the coordinate values of the points passing through the threshold of the upper frequency sweep and the lower frequency sweep exceeds the threshold, not determining the upper frequency sweep and the lower frequency sweep of the same target, and not performing pairing.
Calculating the corresponding frequency value of the matched peak point, and setting the peak coordinate of the first threshold point of the up-scan frequency band in the channel 1 as p1_ up, wherein the corresponding frequency value is f1_ up, the corresponding FFT-transformed data is a _ p1_ up +1j b _ p1_ up, and the phase is
The FFT transformed data of the point corresponding to the upper scanning frequency band in the channel 2 is a _ p2_ up +1j b _ p2_ up, and the phase is
Setting the peak value coordinate of the first threshold passing point of the lower sweep frequency segment in the channel 1 as p1_ down, and setting the frequency value corresponding to the point as f1_ down; wherein: a represents the data value of the I path, b represents the data value of the Q path, a _ p1_ up represents that in the array formed by a + j b, the corresponding coordinate of the peak value point of the threshold crossing is p1_ up, b _ p1_ up represents that in the array formed by a + j b, the corresponding coordinate of the peak value point of the threshold crossing is p1_ up.
The calculation module is used for calculating the time difference between the current time and the current time,
the distance calculation method comprises the following steps: obtaining the frequency value f1_ up of the upper sweep frequency in the channel 1 and the frequency value f1_ down corresponding to the lower sweep frequency according to a formula
Obtaining the distance of the unmanned aerial vehicle to the obstacle target, wherein T is a triangular wave period, B is a frequency modulation bandwidth, and c is the speed of light;
the speed calculation method comprises the following steps: obtaining the frequency value f1_ up of the upper sweep frequency in the channel 1 and the frequency value f1_ down corresponding to the lower sweep frequency according to a formula
Obtaining the speed of the unmanned plane forward obstacle target, wherein f0Is the center frequency;
the angle calculation method comprises the following steps: in channel 1 and channel 2, the phases are respectively calculated according to the respective upper frequency sweeps
And
according to a calculation formula
Obtaining the phase difference delta psi; according to the formula
And calculating the azimuth angle, wherein lambda is the wavelength, and d is the antenna spacing.
The apparatus described in this example corresponds to each of the methods in examples 1 or 2.
Example 4: for the peak processing in the above solutions, this embodiment provides a peak processing method applied to the signal of the unmanned aerial vehicle:
setting a peak point threshold factor α for limiting the absolute value of the difference between the detected threshold-crossing maximum peak point and the maximum peak point appearing in the previous cycle, so that the absolute value of the difference is not greater than the peak point threshold factor α:
the expression is as follows:
|L_max(k)-L_max(k-1)|≤α；
wherein: l _ max (k) is the maximum peak point coordinate of the threshold passing of the k period, L _ max (k-1) is the maximum peak point coordinate of the last period, and k represents the kth moment; v. ofmaxThe maximum flight speed of the unmanned aerial vehicle is shown, lambda is the wavelength of the millimeter wave radar, fs is the sampling rate, and N is the number of points of FFT;
if the absolute value difference value of the threshold-crossing maximum peak point at the moment k and the threshold-crossing maximum peak point at the moment k-1 is within the set range of the threshold factor alpha of the peak point, the peak point of the kth period is considered to be effective; and if the threshold-crossing maximum peak point exceeds the set peak point threshold factor alpha at the moment k, replacing the peak point output at the moment k with the peak point at the moment k-1.
As an explanation of the above technical means, in a time unit of an adjacent period, the peak point calculated in the current period and the peak point of the previous period, if the speed does not change in the adjacent period, the peak point will remain unchanged in the adjacent period, but if the horizontal flying speed of the unmanned aerial vehicle changes in the adjacent period, the horizontal flying speed of the unmanned aerial vehicle will result in the current period changingThe peak point of the period changes to a certain extent in the peak point of the last period, if the unmanned aerial vehicle is close to the target, the number of points of the current period is smaller than the number of points of the last period, if the unmanned aerial vehicle is far away from the target, the number of points of the current period is larger than the number of points of the last period, the change range of the peak point is the designed peak point threshold value factor alpha, the value range selected by the factor is mainly determined by the maximum flight speed of the unmanned aerial vehicle in the adjacent period, namely the formula
Wherein v ismaxThe maximum flight speed of the unmanned aerial vehicle is shown, lambda is the millimeter wave radar wavelength, fs is the sampling rate, and N is the number of points of FFT.
However, if the flight environment of the unmanned rotorcraft changes suddenly, the number of peak points corresponding to the threshold may also continuously exceed the designed threshold factor. If the correction is not carried out, after mutation occurs, the threshold-crossing maximum peak point detected in each period exceeds the set threshold factor, and the threshold-crossing maximum peak point coordinate is corrected to the peak point coordinate at the last moment every time, namely, the value before mutation is also kept by the same value, and the value after mutation cannot be adapted. In order to improve the adaptability of the unmanned aerial vehicle to various environments, a peak point mutation accumulation factor phi is introduced for the unmanned aerial vehicle.
And setting a peak point sudden change accumulation factor phi, wherein the peak point sudden change accumulation factor phi is defined as that if b periods are continuously carried out from the moment k, the value range of b is 5-10, and the threshold-crossing maximum peak point is compared with the threshold-crossing maximum peak point of the previous period and exceeds a threshold factor a, the threshold-crossing maximum peak point calculated at the moment k + b is taken as the threshold-crossing maximum peak point at the moment. In order to ensure the real-time performance of tracking, the value of b is 5-10.
And after the threshold-crossing maximum peak point is obtained in the last step, in order to improve the precision of the measurement of the table system value, a spectrum maximum estimation algorithm for improving the distance measurement precision is provided.
Ideally, the frequency spectrum of the echo difference frequency signal has only one spectral line, but actually, in the using process, due to the barrier effect existing in sampling, the spectral line with the maximum amplitude of the discrete frequency spectrum inevitably shifts the position of a spectral peak, so that a certain error exists between the distance value calculated by the peak point and the actual distance. When a spectral peak is shifted, the central spectral line corresponding to the main lobe peak will be shifted to the left or to the right. If the left peak value is larger than the right peak value in the left and right peak values of the threshold-crossing maximum value peak value point, the position of the central spectral line is between the maximum peak value point and the left peak value point, otherwise, the position is between the maximum peak value point and the right peak value point.
Because the spectrum obtained by FFT calculation samples continuous distance spectrum at equal intervals, the maximum point of the spectrum amplitude is necessarily positioned in the main lobe of the curve, and the main lobe has two sampling points. Setting the coordinates of the threshold-crossing maximum peak point A1 as (a1, k1), wherein a1 represents the value of the threshold-crossing maximum peak point, and k1 represents the amplitude value corresponding to the threshold-crossing peak point; the coordinates of the secondary peak points are A3(A3, k3), the coordinate of the central peak point A is (amax, kmax), and e is amax-a1, the point A1, the coordinate of the point A2 symmetric to the point A is (a2, k1) is (a1+2e, k1), and the zero point A4 of the complex envelope is (a4, k1) is (A3+ e, 0);
wherein: a2, a3 and a4 are the values of the over-threshold maximum peak point of the corresponding point, and k3 and k4 are the amplitude values corresponding to the over-threshold peak point of the corresponding point;
a2, A3 and A4 are approximately a straight line, and the linear relationship is as follows:
order to
Then
Setting error E and deviation E to compare, if | E tint<E, the value of the over-threshold peak point at the moment is the value of the required central peak point, if the deviation is EWhen the error is larger than the set error E,
beta is a correction factor, the value range is 1.5-1.9, and the correction factor is selected from the following reasons: due to the initial time
The coordinate of the point a symmetric point a2 is (a2, k1) — (a1+2E, k1), the abscissa of the point a is symmetric to the abscissa of the point a2 about the maximum peak point under the initial condition, that is, the coordinate of the point a2 is a1+2E, if the deviation E is greater than the set error E, it means that the coordinate of the point a2 is selected too large, that is, the maximum peak point is between a1+2E, and the 2-fold deviation E needs to be reduced. The value principle of the correction factor beta can be selected according to the required E value, if the required precision of E is not high, the correction factor beta can be selected to be 1.9 for correction, if the required precision of E is high, multiple iterations are possibly required to meet the requirement, the correction factor beta needs to be selected to be as small as possible, and 1.5 can be selected for correction. The value of e calculated by the correction factor is changed to calculate the value amax of the central peak point as a1+ e.
As another embodiment, the method further comprises the steps of: distance tracking: setting a threshold factor epsilon, which is used for limiting the absolute value of the difference between the current distance data H (k) and the distance data H (k-1) appearing in the previous period, so that the absolute value of the difference is not larger than the threshold factor epsilon;
the expression is as follows:
the value of | H (k) | -H (k-1) | is less than or equal to epsilon, and the value range of epsilon is 0.8-1.3;
if the absolute value difference value of the data at the k moment and the absolute value difference value at the k-1 moment are within the range of the set threshold factor epsilon, the peak point of the k-th period is considered to be effective; if the data at time k exceeds the set threshold factor epsilon, the data output at time k is replaced with the data at time k-1.
And setting a sudden change accumulation factor theta, wherein the sudden change accumulation factor theta is defined in that if b periods are continued from the time k, and the data are compared with the data of the previous period and exceed a threshold factor theta, the data obtained by resolving the current time are taken as the data of the current time at the time k + b.
As an embodiment, specifically, in the embodiment, for the distance data which is not subjected to the distance tracking or is subjected to the distance tracking, when outputting, the distance value is output by using a sliding window algorithm for the distance data which is output once;
the data at time k is equal to N in the sliding windowcThe average value of the values after the maximum value and the minimum value are removed is used as the final data output, and the calculation formula is
By adopting the peak value tracking algorithm and the tracking algorithm, the abnormal phenomenon of one or more times of data calculation caused by single or multiple times of peak value searching errors can be effectively avoided, for example, in the single peak value searching process, peak value jumping occurs, the peak value difference value between adjacent periods is large, and simultaneously, the large jumping occurs caused by the jumping with the peak value, namely, the jumping range caused by the peak value jumping in the period is far larger than the distance change range caused by one period caused by the speed of the unmanned aerial vehicle. Therefore, the peak tracking and tracking can effectively avoid abnormal values caused by the abnormal peaks, and the stability of the tracked data is effectively improved.
The above description is only for the purpose of creating a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution and the inventive concept of the present invention within the technical scope of the present invention.
Claims (7)
1. The utility model provides a fixed wing unmanned aerial vehicle collision avoidance system radar signal processing apparatus based on millimeter wave radar which characterized in that includes:
the acquisition module is used for AD data acquisition;
the direct current removing module is used for removing direct current;
the window function processing module is used for processing the window function;
the FFT conversion module is used for FFT conversion;
the threshold detection module is used for CFAR threshold detection;
the binary detection module is used for binary detection;
the pairing processing module is used for pairing processing;
the resolving module is used for resolving speed and/or distance and/or angle;
the peak value processing method in the threshold detection module comprises the following steps:
setting a peak point threshold factor α for limiting the absolute value of the difference between the detected threshold-crossing maximum peak point and the maximum peak point appearing in the previous cycle, so that the absolute value of the difference is not greater than the peak point threshold factor α:
the expression is as follows:
|L_max(k)-L_max(k-1)|≤α；
wherein: l _ max (k) is the maximum peak point coordinate of the threshold passing of the k period, L _ max (k-1) is the maximum peak point coordinate of the last period, and k represents the kth moment; v. ofmaxThe maximum flight speed of the unmanned aerial vehicle is shown, lambda is the wavelength of the millimeter wave radar, fs is the sampling rate, and N is the number of points of FFT;
if the absolute value difference value of the threshold-crossing maximum peak point at the moment k and the threshold-crossing maximum peak point at the moment k-1 is within the set range of the threshold factor alpha of the peak point, the peak point of the kth period is considered to be effective; and if the threshold-crossing maximum peak point exceeds the set peak point threshold factor alpha at the moment k, replacing the peak point output at the moment k with the peak point at the moment k-1.
2. The millimeter wave radar-based radar signal processing apparatus of a collision avoidance system for fixed-wing drones, according to claim 1, wherein the acquisition module:
(1) carrying out digital processing on the continuous IQ data in the channel 1 and the channel 2 through AD sampling;
(2) and dividing the data collected in the channel 1 and the channel 2 into upper sweep frequency data and lower sweep frequency data of triangular waves, and removing front part of data points.
3. The millimeter wave radar-based radar signal processing apparatus of a fixed-wing drone collision avoidance system of claim 1, wherein the de-dc module:
(1) respectively calculating the mean values of upper and lower sweep IQ data of the channel triangular wave in the channel 1 and the channel 2;
(2) and subtracting the mean value obtained by the previous step of calculation from each data of the upper and lower sweep IQs of the triangular wave of each channel.
4. The millimeter wave radar-based radar signal processing apparatus of the collision avoidance system for the fixed-wing drone of the invention as set forth in claim 1, wherein the window function processing module performs windowing on the time domain data after the respective dc removal of the upper and lower sweep frequency segments of the triangular wave in the channel 1 and the channel 2, and selects the hanning window and/or the hamming window.
5. The millimeter wave radar-based radar signal processing apparatus of a fixed-wing drone collision avoidance system of claim 1, wherein the threshold detection module:
(1) averaging the complex modulus of each point after the sweep frequency FFT conversion on the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion on the triangular wave in the channel 2, and averaging the complex modulus of each point after the sweep frequency FFT conversion under the triangular wave in the channel 1 and the complex modulus of the corresponding point after the sweep frequency FFT conversion under the triangular wave in the channel 2;
(2) and carrying out CFAR threshold detection on the averaged data.
6. The millimeter wave radar-based radar signal processing apparatus of a fixed-wing drone collision avoidance system of claim 1, wherein the pairing processing module: after CFAR detection and binary detection, pairing the points passing through the threshold of the upper frequency sweep and the lower frequency sweep, and if the difference of the coordinate values of the points passing through the threshold of the upper frequency sweep and the lower frequency sweep exceeds the threshold, not determining the upper frequency sweep and the lower frequency sweep of the same target, and not performing pairing.
7. The millimeter-wave radar-based radar signal processing apparatus of a fixed-wing drone collision avoidance system according to claim 1, wherein the calculation module,
the distance calculation method comprises the following steps: obtaining the frequency value f1_ up of the upper sweep frequency in the channel 1 and the frequency value f1_ down corresponding to the lower sweep frequency according to a formula
Obtaining the distance of the unmanned aerial vehicle to the obstacle target, wherein T is a triangular wave period, B is a frequency modulation bandwidth, and c is the speed of light;
the speed calculation method comprises the following steps: obtaining the frequency value f1_ up of the upper sweep frequency in the channel 1 and the frequency value f1_ down corresponding to the lower sweep frequency according to a formula
Obtaining the speed of the unmanned plane forward obstacle target, wherein f0Is the center frequency;
the angle calculation method comprises the following steps: in channel 1 and channel 2, the phases are respectively calculated according to the respective upper frequency sweeps
And
according to a calculation formula
Obtaining the phase difference delta psi; according to the formula
And calculating an azimuth angle, wherein lambda is the wavelength, d is the antenna spacing, a represents the data value of the path I, b represents the data value of the path Q, a _ p1_ up represents that in an array formed by a + j x b, the corresponding coordinate of the peak value point of the threshold crossing is p1_ up, b _ p1_ up represents that in the array formed by a + j x b, the corresponding coordinate of the peak value point of the threshold crossing is p1_ up.
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