CN105093227A - Traffic flow measuring apparatus and vehicle operation information obtaining method - Google Patents

Abstract

The invention discloses a traffic flow measuring device and a method for obtaining vehicle operation information, comprising: a waveform generator connected in sequence, a directional coupler, a power amplifier, a circulator and an antenna, and a controller connected to the waveform generator, a frequency A synthesizer, a digital signal processor connected to a controller; also includes a first mixer connected to a directional coupler and a frequency synthesizer; also includes a bandpass filter/low noise amplifier connected to a circulator; also includes an intermediate frequency Mixing frequency amplification and data acquisition branch, this device can provide complete real-time vehicle traffic information, the performance of traffic flow measurement is high, and the technical effect is to facilitate the management of driving vehicles.

Description

Device for measuring traffic flow and method for obtaining vehicle operation information

technical field

The invention relates to the field of traffic flow measurement, in particular to a traffic flow measurement device and a method for obtaining vehicle running information.

Background technique

Traditional traffic flow measurement only counts the number of vehicles passing by a certain position on the highway in a certain period of time, but cannot measure the speed and direction of vehicles, nor can it measure the length of vehicles.

The installation method of the existing traffic flow measuring device is shown in Figure 1. The linear frequency modulation continuous wave (LFMCW) radar system is adopted, and the measuring device is installed in a vertical manner. The radial velocity of the vehicle relative to the measuring device is zero, and the device cannot measure To get the speed of the vehicle, only simple traffic flow data statistics can be made, and the real-time prediction effect on the traffic situation is not good. If the measuring device is placed parallel to the road, the measuring instrument can measure the speed of the vehicle, but it cannot distinguish the location of the vehicle. The lanes at the location cannot effectively manage the vehicles in each lane.

To sum up, in the process of realizing the technical solution of the invention in the embodiment of the present application, the inventor of the present application found that the above-mentioned technology has at least the following technical problems:

In the prior art, the existing traffic flow measurement device or method has a single function, can only realize the statistics of the number of vehicles, cannot realize the measurement of the vehicle speed and vehicle length parameters of each vehicle, and cannot provide complete real-time vehicle traffic information technical problems.

Contents of the invention

The invention provides a traffic flow measuring device and a method for obtaining vehicle operation information, which solves the problem that the existing traffic flow measuring device or method has a single function and can only realize the statistics of the number of vehicles, and the vehicle speed and vehicle length parameters of each vehicle The technical problems of not being able to measure and not being able to provide complete real-time vehicle traffic information have achieved the technical effect of having various functions of the device, being able to provide complete real-time vehicle traffic information, having high traffic flow measurement performance, and facilitating the management of driving vehicles.

If the traffic flow device can measure the number of vehicles, the direction of travel, and the speed, it can effectively predict the traffic situation on the road in real time, achieve lane separation and speed limit, punish illegal driving, and effectively guide drivers to drive safely, which is an important aspect of intelligent transportation. component.

Therefore, in order to monitor vehicles in different lanes and different driving directions on the highway, obtain vehicle speed, lane, and vehicle length information, so as to separate lanes and classify speed limit management for vehicles in different lanes, and provide real-time information on vehicles driving on the highway. Information, and effective evidence collection for vehicles traveling in the wrong direction, speeding, and illegally changing lanes. The invention proposes a radar system device and a vehicle information extraction method based on LFMCW.

At present, the traffic flow detection device has a single function, which can only realize the statistics of the number of vehicles, and cannot measure the speed and length parameters of each vehicle, and cannot provide complete real-time vehicle traffic information. Speed information, vehicle type information, and vehicle lane information are used to obtain evidence for vehicle violations and provide correct guidance for vehicle driving. The invention discloses a traffic flow detection radar device, and gives details of the vehicle based on the radar device. Extraction method for running information.

In order to solve the above technical problems, the embodiment of the present application provides the structure of the traffic flow detection radar device of the present invention relative to the autodyne receiver, as shown in Figure 2. The difference is that the local oscillator signal is generated in a different way. The radar receiver structure is to transmit the signal directly as a local oscillator signal after being coupled by a coupler; and the traffic flow detection radar device of the present invention is to utilize the intermediate frequency signal produced by the frequency synthesizer as shown in accompanying drawing 3 as a local oscillator The signal and the transmitted signal are mixed once through the first mixer, and the mixed signal obtained is shown in Figure 4, and then the first mixed signal is filtered and amplified, and the radar echo signal is passed through the second mixer Secondary frequency mixing is performed to obtain radar echo IF signals whose IF frequency is not zero. The IF signals are band-pass filtered, amplified, and analog-to-digital converted to obtain digital IF signals, and then digitally down-converted (DDC) to obtain digital baseband complex signals. Signal. The effect of this double frequency mixing is: the digital baseband complex signal obtained after processing the intermediate frequency echo signal obtained after the two times of mixing can distinguish the direction of the vehicle, so that it can be measured by a traffic flow detection radar device The traffic flow of two-way multiple lanes and the movement information of vehicles on each lane. Including the following steps:

Step 1. Generate an FM continuous wave in the mth period of a coherent processing interval (CPI). The generated FM continuous wave is divided into two channels, A and B. The A channel is transmitted through the antenna, and the B channel and the intermediate frequency produced by the frequency synthesizer The signal is mixed to obtain signal C;

Receive the echo signal of the speed measurement target through the antenna, and mix the echo signal with the C-channel signal to obtain the intermediate frequency signal SI(t,m);

Step 2. Convert the intermediate frequency signal into a digital signal, and obtain the complex baseband signal sequence S[n,m] of the digital signal through digital quadrature down-conversion;

Step 3. Perform FFT on the fast time dimension of S[n,m], that is, the n dimension, and then perform FFT to obtain the sequence S[F1,m]. Performing FFT after dimension windowing can obtain the sequence X[F1,F2] after 2D-FFT;

Step 4. Use the constant false alarm threshold to detect the sequence after 2D-FFT, divide the range gates by lanes, and find the normalized frequency F corresponding to the peak point in the range gates judged to have targets, so as to solve the corresponding The speed information of the target in the lane is obtained by calculating the echo power of the peak point to obtain the RCS of the target vehicle.

Step 5. Through continuous observation of multiple CPIs, the number of CPIs of vehicles in each lane appearing in the radar irradiation area is detected through constant false alarm, and the vehicle length of the target vehicle is calculated in combination with the speed of the target and the width of the radar beam. Combined with the vehicle length information and the RCS of the vehicle, the model information of the vehicle is obtained.

The invention also discloses a traffic flow detection device, which includes a sequentially connected waveform generator, directional coupler, power amplifier, circulator and antenna, and also includes a controller connected to the waveform generator, a frequency synthesizer, and a controller connected digital signal processor;

It also includes a first mixer connected to the directional coupler and the frequency synthesizer;

Also includes a bandpass filter/low noise amplifier connected to the circulator;

It also includes an intermediate frequency mixing amplification and data acquisition branch, and the intermediate frequency amplification and data acquisition branch is composed of a second mixer, a bandpass filter, an amplifier, and an AD converter connected in sequence;

The output terminal of the first mixer is connected to one of the input terminals of the second mixer through a filter/amplifier, and the output terminal of the band-pass filter/low noise amplifier is connected to the other input terminal of the second mixer , the output end of the AD converter is connected to a digital signal processor, and the sampling clock input end of the AD converter is connected to a frequency synthesizer.

Preferably, the waveform generator is composed of a direct digital frequency synthesizer, a phase-locked loop and a frequency multiplier connected in sequence, and the frequency control terminal of the direct digital frequency synthesizer and the phase-locked control terminal of the phase-locked loop are respectively connected to the control The frequency input terminal of the direct digital frequency synthesizer is used as the input terminal of the waveform generator, and the output terminal of the frequency multiplier is used as the output terminal of the waveform generator.

Preferably, the waveform generator is composed of a direct digital frequency synthesizer, a frequency synthesizer, N mixers, and N+1 bandpass filters, and the mixers and bandpass filters are connected at intervals, the first The input end of the band-pass filter is connected to the direct digital frequency synthesizer, the local oscillator frequency input end of each mixer is connected to an output end of the frequency synthesizer, and the output end of the last band-pass filter is used as the signal of the waveform generator At the output terminal, N is a positive integer.

Preferably, the superheterodyne receiver structure of the device, compared with the traditional self-beating structure, has obtained a non-zero intermediate frequency signal due to the superheterodyne structure, so that the complex baseband signal can be obtained by using digital down-conversion technology, The direction information of the vehicle motion is preserved.

In addition, the installation method of the traffic flow detection radar device described in this invention needs to make specific requirements, and its schematic diagram is shown in Figure 5 . On the horizontal plane, the radar irradiation direction and the lane can neither be perpendicular nor parallel, and the included angle can be any other angle between 0° and 180°. The reason for setting the radar irradiation angle in this way is: on the horizontal plane, when the irradiation direction is perpendicular to the lane, the radial velocity of the vehicle relative to the radar is 0, and the speed of the vehicle cannot be detected; when the radar irradiation direction is parallel to the lane, it can be measured The speed of the vehicle can be determined, but the vehicles in different lanes cannot be distinguished. After meeting the requirements of the radar irradiation direction, the traffic flow detection radar can measure the speed of the vehicle and the specific lane where it is located, and can provide comprehensive real-time traffic information.

Preferably, the included angle between the radar irradiation direction and the lane is selected as an angle between 15 degrees and 75 degrees, so that the vehicle can have a relatively large radial velocity and can distinguish the lane in the distance dimension.

Based on the highway traffic flow detection radar device described in the present invention, the present invention proposes a corresponding vehicle operation information extraction method. The method combines digital down-conversion (DDC) technology and two-dimensional FFT (2D-FFT) technology to obtain vehicle motion information. First, the baseband complex signal is obtained through DDC technology, and then the baseband signal is subjected to 2D-FFT operation, and the range gate divided by the lane is used for target detection, so as to obtain the speed of the vehicle in the corresponding lane, and the target is obtained through the echo peak power in the corresponding range gate. Radar cross-sectional area (RCS) information, and then measure the length of the vehicle through the radar beam width, vehicle speed, and the number of coherent processing interval (CPI) of the target in the corresponding lane, and combine the RCS information to judge the vehicle type, so as to divide the vehicle into lanes manage.

Compared with the prior art, the present invention has the following advantages: the intermediate frequency echo signal is obtained by twice mixing, the processing of the intermediate frequency echo signal can distinguish the driving direction of the vehicle, and the two-way lane can be detected at the same time; not only can the size information of the traffic flow be obtained, Vehicle-specific movement information can also be obtained, including the speed at which the vehicle is traveling, the lane it is in, and the type of vehicle. Therefore, the highway traffic flow measurement radar of the present invention can obtain more vehicle operation information than existing traffic flow products, and the performance of the traffic flow measurement system is improved.

Description of drawings

Fig. 1 is a schematic diagram of the spatial geometric relationship between the existing traffic flow device and the road surface;

Figure 2 is a schematic block diagram of the LFMCW radar with self-beating structure;

Fig. 3 is a structural block diagram of the traffic flow measuring device;

Fig. 4 is a schematic diagram of the local oscillator signal after the first frequency mixing;

Fig. 5 is a schematic diagram of the spatial geometric relationship between the traffic flow measurement device and the road surface;

Fig. 6 is the structural representation of waveform generator;

Figure 7 is a schematic diagram of the 2D-FFT spectrum after windowing;

Figure 8 is a schematic diagram of distance dimension slices after windowing;

Figure 9 is a schematic diagram of velocity dimension slices after windowing;

Fig. 10 is a schematic diagram of the echo power peak value of lane 3.

Detailed ways

The invention provides a traffic flow measuring device and a method for obtaining vehicle operation information, which solves the problem that the existing traffic flow measuring device or method has a single function and can only realize the statistics of the number of vehicles, and the vehicle speed and vehicle length parameters of each vehicle The technical problems of not being able to measure and not being able to provide complete real-time vehicle traffic information have achieved the technical effect of having a variety of device functions, being able to provide complete real-time vehicle traffic information, having high performance in measuring traffic flow, and facilitating the management of driving vehicles.

In order to better understand the above-mentioned technical solution, the above-mentioned technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

Embodiment one:

In the first embodiment, the specific implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 3 is a schematic structural block diagram of the traffic flow measurement radar system of the present invention.

The transmitting part includes a waveform generator 3, a directional coupler 4, a power amplifier 5, a circulator 7 and an antenna 6, wherein the waveform generator 3 requires a controller 1 to write a control word to it to generate the required frequency-modulated continuous wave (FMCW) waveform, and the FMCW signal is input to the directional coupler 3, the above-mentioned directional coupler sends one signal to the first mixer 9, and the frequency synthesizer generates one intermediate frequency signal and sends it to the other input end of the first mixer 9 , the output signal of the first mixer 9 is used as a local oscillator signal after being filtered and amplified; at the same time, the above-mentioned directional coupler 4 outputs another signal, and the output signal transmits the FMCW signal through the circulator 7 and the antenna 6.

After the antenna 6 receives the echo signal, it is output to the low noise amplifier (LNA)/bandpass filter 8 through the circulator 7, and enters the second mixer 11, and the above-mentioned local oscillator signal is input to another part of the second mixer 11 One input end, through the above operation, the received radio frequency signal is converted into an intermediate frequency signal, and the intermediate frequency signal is input to the bandpass filter 12 and the amplifier 13 in turn, and then input to the ADC14 to convert the input analog signal into a digital signal.

The signal processing part includes a digital signal processor 15, wherein the digital signal output by the receiving part enters the digital signal processor 15, and the digital signal processor 15 performs quadrature down-conversion on the received digital signal, and then performs 2D-FFT to solve the problem according to The speed information of the vehicle in the distance unit divided by the vehicle is combined with the vehicle speed, beam width, and the number of coherent processing interval (CPI) of the target in the corresponding lane to measure the vehicle length information and then combine the echo intensity to judge the vehicle type, so as to obtain at the same time The target's speed, lane, and vehicle type information.

As shown in Figure 6, it is a block diagram of the internal structure of a specific implementation of the waveform generator. The waveform generator can generate frequency-modulated continuous waves, and the controller 1 controls the timing of the clock and the frequency of the DDS (Direct Digital Frequency Synthesizer). The word M is controlled to make it generate the frequency-modulated continuous wave (LFMCW) intermediate frequency signal of the required bandwidth range, and the spurious components are filtered out through the band-pass filter. The implementation mode in Fig. 6 adopts three band-pass filters and two mixers The frequency converters are interleaved. The local oscillator frequency of the mixer is generated by the frequency synthesizer and up-converted. After two-stage up-conversion, the RF signal with the carrier frequency f ₀ and the bandwidth B can be obtained. The up-conversion requires The local oscillator signal is generated by the frequency synthesizer 2.

The vehicle flow information acquisition method based on the above-mentioned device comprises the following steps:

Step 1. Generate FM continuous wave in the mth period of a CPI, the generated FM continuous wave is divided into two paths, one path is transmitted through antenna, and the other path generates local oscillator signal through mixer;

Receive the echo signal of the vehicle through the antenna, mix the echo signal with the above-mentioned intermediate frequency signal after passing through the LNA and filter, and obtain the intermediate frequency signal SI(t,m);

Take the installation method of the traffic flow detection radar device shown in FIG. 5 as an example. Let the modulation period of LFMCW signal be Tr, the initial carrier frequency of the transmitted signal is f0, the bandwidth is B, the frequency range of the signal is [f0, f0+B], and the time delay of the echo signal relative to the transmitted signal is τ. At the same time, due to the Doppler frequency shift caused by the relative motion of the target and the radar, the frequency changes, and the corresponding effective receiving window is [τ, Tr].

The output of one end of the directional coupler is the transmit signal, which is set to St(t,m), then the expression of the transmit signal is:

Where At is the amplitude of the transmitted signal, u=B/Tr is the frequency modulation slope, and φ0 is the initial phase.

For the echo signal, let the echo signal be Sr(t,m), and the expression of the echo signal is:

Where Ar is the amplitude of the echo signal.

The output of the other end of the directional coupler is mixed with the intermediate frequency signal generated by the frequency synthesizer and then filtered and amplified to obtain the local oscillator signal as:

The intermediate frequency signal obtained by mixing the echo signal with the local oscillator signal is:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;\&tau;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;\&tau;kT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&le;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Assuming that the distance between the target and the radar is R0, moving towards the radar with a radial velocity v0, the echo delay

1. $\mathrm{\&tau;}=\frac{2\&lsqb;R_0-\left(v_{0}co\mathrm{the\; s}\mathrm{\&theta;}\right)t\&rsqb;}{c}---\left(5\right)$

Where c is the speed of light, substituting (5) into (4) can get:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&mu;v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&mu;R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>\\ \begin{array}{cc}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; v</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>& {\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&le;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\end{array}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

The transmission bandwidth B is usually at the MHz level, and the transmission frequency f0 is in the radio frequency range, reaching tens of GHz. Therefore, according to B<<f0, v0<<c, it can be obtained

According to formula (7) and formula (8), formula (6) is simplified to get the expression of intermediate frequency signal:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&mu;R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

where kT _r +τ≤t≤(k+1)T _r .

Step 2. Convert the baseband signal SI(t,m) into a digital signal, and perform digital quadrature down-conversion on the sampled signal to obtain its complex baseband signal.

Sampling the baseband signal SI(t,m) with a positive frequency modulation slope, setting the sampling rate as fs, and the corresponding sampling interval as Ts, which is equivalent to t=mT _r +nT _s , where n=0,1,...,N -1, N is the number of sampling points in each period, substituting into formula (9) to obtain the expression of the intermediate frequency signal after sampling:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&mu;R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

The expression of the complex baseband signal can be obtained by digitally down-converting the signal as follows:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&mu;R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

Step 3. Perform FFT on the fast time dimensional window to obtain its fast time dimensional spectrum. After collecting the last cycle of CPI, that is, the signal of the Mth cycle, perform FFT on the slow time signal to obtain a CPI echo signal spectrum.

The echo spectrum of the mth cycle can be obtained by doing Nf-point FFT after adding a window to the n dimension of formula (11):

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&lsqb;</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \}</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

Where wN is the discrete Fourier transform of the window function, and the '*' operation represents the convolution and operation.

After collecting the signal of the M-th period, the FFT of the Mf point after windowing the m dimension can be obtained:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \}</span>$ $<span\; class="notranslate">\; \&lsqb;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \&lsqb;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

Where wM is the discrete Fourier transform of the window function, and the '*' operation represents the convolution and operation.

Step 4. Perform range gate division on the results of the 2D-FFT in the fast time dimension according to the lane information, and use constant false alarm (CFAR) to detect whether there is a target vehicle in each lane. If there is, then in the target spectrum P(kR,kv) Find the normalized frequency of the slow time dimension corresponding to the point where the k-th range gate, that is, the corresponding k-th lane is judged as the target exists Solve the speed of the target to be measured, which is shown in the following formula.

$\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

From formula (17), we can get:

${\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; ck</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; MT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

Step 5. Through continuous observation of multiple CPIs, use constant false alarm detection to determine the number of CPIs P that vehicles in each lane fall into the radar irradiation area. Let the width of each lane be W, and the vertical distance between the radar and the first lane be S , and the radar beam width is β, then the vehicle length of the kth lane can be calculated as:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; PT</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

A specific embodiment is given below.

Using the vehicle information acquisition method shown above, the transmission waveform adopts sawtooth linear frequency modulation continuous wave, and the receiver adopts DDC to obtain the complex baseband signal of the echo.

In this embodiment, the actual scene is shown in Figure 5, and the simulation scene uses 6 lanes. According to the national standard, the width of the 6 lanes is 2*11.25m, and the included angle between the main radar beam and the horizontal direction of the road surface is 60°, which corresponds to The vertical distance in the horizontal direction of the road surface is 5m. The range of distance measured by radar is 10m-55m, and the range of speed measurement is 0m/s-70m/s. The modulation period Tr of the transmitted signal is 50μs, the carrier frequency f0 = 35GHz, the FM bandwidth B = 75MHz, the intermediate frequency sampling rate fs = 5MHz, the corresponding sampling interval Ts = 0.2μs, the accumulation period of a CPI is 128, and the antenna adopts beam width 1° conical horn antenna. At the same time, let the echo intermediate frequency signal-to-noise ratio SNR=-10dB, and the simulated vehicles are divided into three types: large trucks, small trucks, and small cars. The RCS of large trucks is twice that of small trucks, and the RCS of small trucks is 2 times that of small cars. times. The vehicle types of the six lanes are large trucks and small trucks. Cars, trucks, trucks, cars. The speed of the six lanes is set to 10m/s, 33m/s, 15m/s, -20m/s, -38m/s, -40m/s in turn, and the distance between the vehicles in the six lanes and the radar is 14.5000m, 21.2500 m, 28.0000m, 37.9000m, 44.6500m, 49.6000m, and the lengths of the vehicles leaving a lane are: 6m, 10m, 15m, 5.5m, 8.8m, 14m. In this scenario, assuming that at time t=0, vehicles in six lanes have just entered the radar irradiation area, the number of slow-time Fourier transform points is 512, and the number of fast-time Fourier transform points is 2048. The window function added before FFT is hanning window. Figure 7 shows the frequency spectrum after performing 2D-FFT on the echo signal, Figure 8 shows the distance-dimension slice, and Figure 9 shows the velocity-dimension slice. In practical application, the width of the lane and the location of the radar are known, and the detection range gate is divided according to the distance of the lane, the position of the radar and the width of the lane, and the threshold judgment is made in each distance gate to obtain each Vehicle speed, echo amplitude and other information of the lanes, the measured vehicle speeds of the six lanes are: 9.7098m/s, 32.8125m/s, 14.7321m/s, -20.4241m/s, -5.3571m/s, -40.5134 m/s, which is close to the real speed. By continuously observing the echoes of each distance unit of 512 CPIs, and adopting the constant false alarm method to judge whether there is a target, the time when the vehicle falls into the radar irradiation area can be obtained, and combined with the measured speed of the vehicle in each CPI, it can be obtained The speed of the target, the echo peak value of 512 consecutive CPIs in the third lane is shown in Figure 10. From the constant false alarm, it can be judged that the time of the vehicle in the radar irradiation interval is 162 CPIs, and the vehicle length can be solved as: 14.8799m .

Similarly, the vehicle lengths of the six lanes can be obtained in sequence: 5.8991m, 10.3391m, 14.8799m, 5.8742m, 9.5407m, and 14.6915m, which are close to the real vehicle length. Normalized with the RCS of large trucks, the RCS of vehicles with 6 lanes is 0.2548, 0.5884, 1.0000, 0.2899, 0.4565, and 0.9296. Close to the real RCS. Therefore, through the device and the measuring method, the lane information, speed information and vehicle type information of the target vehicle can be obtained. Furthermore, by monitoring the number of vehicles in the lane in real time and judging whether there are vehicles in the lane through the constant false alarm, the traffic flow information of the entire lane can be effectively obtained.

The steps of the methods or algorithms described in the embodiments disclosed in the present invention can be directly implemented by hardware, software modules executed by a processor, or a combination of both. Software modules can be placed in random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other Any other known storage medium.

The foregoing is a preferred embodiment of the present invention. The specific parameters in the described embodiment and the embodiment are only for clearly expressing the inventor's invention verification process, and are not intended to limit the scope of patent protection of the present invention. The patent protection scope of the present invention The scope of protection is still subject to the claims, and all equivalent structural changes made by using the description and drawings of the present invention should be included in the scope of protection of the present invention in the same way.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (8)

1. A traffic flow measurement device, characterized in that the device comprises: It includes a waveform generator, a directional coupler, a power amplifier, a circulator and an antenna connected in sequence, a controller connected to the waveform generator, a frequency synthesizer, and a digital signal processor connected to the controller; it also includes a directional coupling The first mixer connected to the device and the frequency synthesizer; also includes a band-pass filter/low noise amplifier connected to the circulator; also includes an intermediate frequency mixing amplifier and a data acquisition branch, and the intermediate frequency amplification and data acquisition branch are composed of A second mixer connected in sequence, a bandpass filter, an amplifier, and an AD converter; the output terminal of the first mixer is connected to one of the input terminals of the second mixer through a filter/amplifier, The output end of the band-pass filter/low noise amplifier is connected with the other input end of the second mixer, the output end of the AD converter is connected with the digital signal processor, and the sampling of the AD converter is The clock input terminal is connected with the frequency synthesizer. 2. device according to claim 1, is characterized in that, described waveform generator is made up of direct digital frequency synthesizer, phase-locked loop and frequency multiplier connected successively, the frequency control end of described direct digital frequency synthesizer 1. The phase-locked control terminals of the phase-locked loop are respectively connected to the controller, the frequency input terminal of the direct digital frequency synthesizer is used as the input terminal of the waveform generator, and the output terminal of the frequency multiplier is used as the output terminal of the waveform generator. 3. The device according to claim 1, wherein the waveform generator is composed of a direct digital frequency synthesizer, a frequency synthesizer, N mixers, and N+1 bandpass filters, and the mixer The frequency converter and the band-pass filter are connected at intervals, the input end of the first band-pass filter is connected with the direct digital frequency synthesizer, the local oscillator frequency input end of each mixer is connected with an output end of the frequency synthesizer, and the end band The output terminal of the pass filter is used as the signal output terminal of the waveform generator, and N is a positive integer. 4. The device according to claim 1, characterized in that, by means of the first mixer, the device is able to preserve the direction information of the vehicle's motion. 5. The device according to claim 1, wherein the included angle between the radar irradiation direction of the traffic flow measuring radar device and the lane is selected as an angle between 15 degrees and 75 degrees. 6. A method for obtaining vehicle operation information, characterized in that the method comprises: First, the baseband complex signal is obtained by digital frequency conversion; Then perform two-dimensional FFT operation on the baseband signal, and perform target detection on the range gates divided by lanes, so as to obtain the speed of the vehicle in the corresponding lane, and obtain the radar cross-sectional area information of the target through the echo peak power in the corresponding range gate; Then the length of the vehicle is measured by the radar beam width, vehicle speed, and the number of coherent processing intervals of the target in the corresponding lane, and the vehicle running information is obtained by combining the radar cross-sectional area information of the target, and then the corresponding model is judged, so that the vehicle is carried out. Lane management. 7. method according to claim 6, is characterized in that, utilizes digital frequency conversion to obtain baseband complex signal, specifically: Use the intermediate frequency signal generated by the frequency synthesizer as the local oscillator signal to perform a frequency mixing with the transmitted signal to obtain the mixed signal; Then, the primary mixing signal is filtered and amplified and then mixed with the radar echo signal for the second time to obtain the radar echo intermediate frequency signal whose intermediate frequency is not zero; The intermediate frequency signal is band-pass filtered, amplified, and analog-to-digital converted to obtain a digital intermediate frequency signal, and then digitally down-converted to obtain a digital baseband complex signal. 8. The method according to claim 7, wherein obtaining vehicle operation information specifically comprises: Step 1: Generate FM continuous wave in the m-th period of a coherent processing interval. The generated FM continuous wave is divided into two channels, A and B. The A channel is transmitted through the antenna, and the B channel is mixed with the intermediate frequency signal generated by the frequency synthesizer. The signal C is obtained frequently, the m is a positive integer, and CPI is a coherent processing interval; Receive the echo signal of the speed measurement target through the antenna, and mix the echo signal with the C-channel signal to obtain the intermediate frequency signal SI(t,m); Step 2: convert the intermediate frequency signal into a digital signal, and obtain the complex baseband signal sequence S[n,m] of the digital signal through digital quadrature down-conversion; Step 3: Perform FFT on the fast time dimension of S[n,m], i.e. the n dimension, and add a window to obtain the sequence S[F1,m]. Performing FFT after windowing can obtain the sequence X[F1,F2] after 2D-FFT; Step 4: Use the constant false alarm threshold to detect the sequence after 2D-FFT, divide the range gate by lane, find the normalized frequency F corresponding to the peak point in the range gate judged to have a target, and then calculate the corresponding The speed information of the target in the lane, the RCS of the target vehicle is obtained by calculating the echo power of the peak point, and the RCS is the radar cross-sectional area of the target; Step 5: Through continuous observation of multiple CPIs, the number of CPIs of vehicles in each lane appearing in the radar irradiation area is detected through constant false alarm, and the vehicle length of the target vehicle is calculated based on the speed of the target and the width of the radar beam, and combined with the vehicle length information Together with the RCS of the vehicle, the model information of the vehicle is obtained.