CN116223838A - Cross-correlation radar flow velocity meter and radar signal denoising method - Google Patents

Abstract

The invention provides a cross-correlation radar flow velocity meter and a radar signal denoising method, which relate to the technical field of fluid measurement and comprise at least two sets of radars with the same working frequency, wherein the two sets of radars are used for alternately receiving and transmitting, the alternating frequency of the radars is larger than the Doppler signal frequency generated by the river surface flow velocity, the corresponding radar signals are obtained through the at least two radars with the same working frequency and the alternating frequency is larger than the Doppler signal frequency generated by the river surface flow velocity, and the signal-to-noise ratio is greatly improved through the repeated accumulation cross-correlation of the radar signals.

Description

Cross-correlation radar flow velocity meter and radar signal denoising method

Technical Field

The invention relates to the technical field of fluid measurement, in particular to a radar signal denoising method and a radar signal denoising method.

Background

The existing flowmeters are similar to those explained in chinese patent application for invention (CN 109001723 a).

Conventionally, signals are synchronously transmitted and received by using a radar, and the received signals are processed, so that Doppler signals of the river surface flow velocity are analyzed, and the river surface flow velocity information is calculated.

However, the radar flow rate meter has great influence on the speed measurement result due to the influence of the environment in the use process, under the condition that the water surface is extremely calm or the flow rate is extremely low, the radar signal is reflected by the water surface like a mirror surface, the Doppler signal intensity of the doped water flow information which can be fed back is extremely weak and even weaker than the noise of the radar, so that the flow rate information in the echo information is completely covered by the noise of the radar and the environmental noise, and under the condition, the radar flow rate meter cannot measure the flow rate information of the water surface.

The above-mentioned current situation causes that the radar flow meter cannot work normally in the case that the detectable signal is weak.

Disclosure of Invention

Aiming at the limitations of the radar flow velocity meter, the technical problem of the invention is to provide a radar signal denoising method and a radar signal denoising method.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

in one aspect, the present application provides a cross-correlation radar flow meter: the system comprises at least two sets of radars with the same working frequency, wherein the two sets of radars alternately transmit and receive, and the alternating frequency of the radars is greater than the Doppler signal frequency generated by the river surface flow velocity.

Specifically, the radars all adopt independent local vibration sources.

On the other hand, the application also provides a radar signal denoising method, which comprises the following steps:

s1: the two radars alternately transmit and receive the same water surface to be detected to obtain respective signals Spe1 and Spe2;

s2: performing FFT conversion on Spe1 and Spe2 respectively to obtain spectrum signals SF1 and SF2;

s3: performing conjugate multiplication on SF1 and SF2 to obtain a primary cross-correlation signal result X;

s4: repeating S1-S3 to obtain signal result set { X ] ₁ ；X ₂ ；X ₃ ……X _n };

S5: the signal result set is accumulated.

According to the method, the radar with at least two same working frequencies alternately receives and transmits, and simultaneously the alternating frequency is larger than the Doppler signal frequency generated by the river surface flow velocity, so that the corresponding radar signal is obtained, and the signal to noise ratio is greatly improved through repeated accumulation cross correlation of the radar signal.

Drawings

The invention and its features, aspects and advantages will become more apparent from the detailed description of non-limiting embodiments with reference to the following drawings. Like numbers refer to like parts throughout. The drawings are not intended to be drawn to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a block diagram of a radar system of the present invention;

fig. 2 is a diagram of a dual radar alternating waveform.

Detailed Description

The invention will now be further described with reference to the accompanying drawings and specific examples, which are not intended to limit the invention.

As shown in fig. 1, a cross-correlation radar flow rate meter: the system comprises at least two sets of radars with the same working frequency, wherein the two sets of radars alternately transmit and receive, and the alternating frequency of the radars is greater than the Doppler signal frequency generated by the river surface flow velocity.

The application uses two sets of radio frequency transceiver circuits, works on the same work evaluation rate, and the transceiver antennas point to the same measuring area.

In order to ensure that the two sets of transceiver circuits are not affected by each other, the two sets of transceiver circuits need to work alternately, and the alternating frequency is far greater than the Doppler signal frequency generated by the river flow velocity, so that the two sets of transceiver circuits can be considered to obtain the same flow velocity signal, the respective noise of the two sets of transceiver circuits is not related to each other, the signals output by the two sets of transceiver circuits are subjected to cross-correlation accumulation, the accumulation frequency is N, and the improvement of the signal to noise ratio can be obtained

Multiple times.

The enabling signal controlling the radar operation is G, the frequency is Fg, and the enabling process is controlled and can be regarded as the multiplication of the Doppler signal S and 0 or 1. The duty cycle is close to 0.5.

Performing series expansion on the G signal:

after enabling control, the output signal is S _g ,

S _g = S * G

Because of the frequency F of the enable signal _g Far greater than the signal frequency F _s Therefore, at maximum F _s A low-pass filter with cut-off frequency, which can filter out all frequencies as F _g And harmonic components thereof.

LPF(Sg) = 0.5 * S

The above description shows that by controlling the signal path using the enable signal having a frequency much greater than the signal frequency, the signal amplitude is reduced by 0.5 times, the signal composition is unchanged, which is why the alternating frequency of the radar is required to be greater than the Doppler signal frequency generated by the river flow velocity

Specifically, the radars all adopt independent local vibration sources.

The local oscillation sources L0 used by the two sets of receiving and transmitting circuits are independent local oscillation sources, so that the phase noise of the two local oscillation sources is uncorrelated. Meanwhile, the frequency difference of the two local oscillation sources is smaller than a certain value, so that the correlation of Doppler signals output by the two local oscillation sources can be ensured. Good correlation can be considered if the two sets of signals remain with a phase error of less than 5 °.

In actual operation, assuming that the distance from the radar to the water surface is R, F0 is the transmitting frequency, and c is the light speed, the relative error k between the two vibration sources can be expressed as:

for example, r=10m, f ₀ At 24ghz, k=5.75×10 ^-5 This accurate frequency reference is achievable, in the case of 25mhz,1ppm accurate TXCO. So the relative error of the signals is controlled to be 10 ^-5 This range is industrially easy to implement.

On the other hand, the application also provides a radar signal denoising method, which comprises the following steps:

s1: the two radars alternately transmit and receive the same water surface to be detected to obtain respective signals Spe1 and Spe2;

s2: performing FFT conversion on Spe1 and Spe2 respectively to obtain spectrum signals SF1 and SF2;

s3: performing conjugate multiplication on SF1 and SF2 to obtain a primary cross-correlation signal result X;

s4: repeating S1-S3 to obtain signal result set { X ] ₁ ；X ₂ ；X ₃ ……X _n };

S5: the signal result set is accumulated.

The signal Spe1 is a complex signal and is composed of a real part I1 and an imaginary part Q1. The same reason Spe2 is composed of a real part I2 and an imaginary part Q2.

The signals output by the two receivers can be expressed as:

Spe1 = S + N1 Spe2 = S + N2

s is a common Doppler signal, and N1 and N2 are independent noise because the two receiving and transmitting systems use time-sharing work and independent local vibration sources.

The cross-correlation processing process comprises the following steps:

SF1 is the spectrum signal after Spe1 has undergone FFT conversion, and SF2 is the spectrum signal after Spe2 has undergone FFT conversion.

SF1 = FFT(Spe1) SF2 = FFT(Spe2)

SF1 and SF2 conjugate multiplication

A primary cross-correlation result is obtained.

N groups of cross-correlation results are accumulated, and the improvement of the signal to noise ratio can be obtained

Multiple times.

As shown in fig. 2, in actual use, the working time of two radars is slightly shorter than the silence time, so that the radars are prevented from receiving echoes of each other, and the accuracy of measurement is ensured.

The foregoing describes preferred embodiments of the present invention; it is to be understood that the invention is not limited to the specific embodiments described above, wherein devices and structures not described in detail are to be understood as being implemented in a manner common in the art; any person skilled in the art will make many possible variations and modifications, or adaptations to equivalent embodiments without departing from the technical solution of the present invention, which do not affect the essential content of the present invention; therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.

Claims (3)

1. Cross-correlation radar flow rate meter: the method is characterized in that: the system comprises at least two sets of radars with the same working frequency, wherein the two sets of radars receive and dispatch alternately, and the alternating frequency of the radars is greater than the Doppler signal frequency generated by the river surface flow velocity.

2. The cross-correlation radar flow meter of claim 1, wherein: the radars all adopt independent local vibration sources.

3. The radar signal denoising method is applied to the cross-correlation radar flow velocity meter according to any one of claims 1-2, and is characterized in that: the method comprises the following steps:

s1: the two radars alternately transmit and receive the same water surface to be detected to obtain respective signals Spe1 and Spe2;

s2: performing FFT conversion on Spe1 and Spe2 respectively to obtain spectrum signals SF1 and SF2;

s3: performing conjugate multiplication on SF1 and SF2 to obtain a primary cross-correlation signal result X;

s4: repeating S1-S3 to obtain signal result set { X ] ₁ ；X ₂ ；X ₃ ……X _n };

S5: the signal result set is accumulated.

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