CN109932710B - Long-distance target speed correction method based on sawtooth LFMCW waveform system speed measurement radar - Google Patents

Abstract

The invention relates to a remote target speed correction method based on a sawtooth LFMCW waveform system speed measurement radar, which comprises the following steps: fast time dimension FFT measures the target distance; obtaining Doppler frequency shift and long-distance echo frequency shift by slow time dimension FFT; and correcting the carrier frequency to obtain the speed value of the remote target. The correction method of the invention can fundamentally solve the error generated when the radar slow time dimension FFT is calculated by the linear frequency modulation continuous wave system on the long-distance target and the large frequency modulation slope, has small resource consumption in signal processing, is easy to realize, and can be widely used in the phase-coherent system LFMCW radar.

Description

Long-distance target speed correction method based on sawtooth LFMCW waveform system speed measurement radar

Technical Field

The invention belongs to the technical field of radar signal processing, and particularly relates to a remote target speed correction method based on a sawtooth LFMCW waveform system speed measurement radar.

Background

Linear Frequency Modulated Continuous Wave (LFMCW) radar has high range resolution and range accuracy, and has more obvious advantages in low range blind area than pulse system radar.

The saw-toothed LFMCW waveform is shown in fig. 1 below.

The LFMCW radar transmit signal model may be expressed as:

s ₁ (t)＝cos(2πf ₀ t+πμt ² )，0≤t≤T _e (1)

wherein μ = B/T _e Mu is LFM slope, B is bandwidth, T _e Frequency modulation period is the sweep frequency period; f. of ₀ Is the start frequency (carrier frequency) of the chirp.

Assuming that there is a point scatterer at a distance R, the radar receives its echo signal as:

s _r (t)＝acos[2πf ₀ (t-Δτ)+πμ(t-Δτ) ² ]，0≤t-Δτ≤T _e (2)

in the formula, a is a signal amplitude, which is related to a target radar scattering cross section (RCS), a distance and an antenna gain; Δ τ =2R/c is the time delay and c is the speed of light.

The reference signal input by the mixer is:

s _ref (t)＝cos(2πf _r0 +πμt ² )，0≤t≤T _e (3)

in the formula, f _r0 For the start frequency of the reference signal LFM, let f be _r0 ＝f ₀ 。

The complex signal model after the frequency mixing and the low-pass filtering of the received signal and the reference signal is as follows:

the instantaneous frequency of the signal is:

the above equation shows that the range of the target is proportional to the instantaneous frequency. So that the received signal is sampled and the sample sequence is FFT-ed at frequency f _i The peak position of (a) corresponds to a target distance of

In the actual LFMCW system radar, fast time dimension FFT is carried out in a frequency sweep section, and the target distance is calculated by the frequency peak value according to the formula (6). And performing slow time dimension FFT between every two frequency scanning bands, wherein the frequency peak value corresponds to the target speed.

However, when the sawtooth LFMCW waveform is used for speed measurement, the remote target causes carrier frequency change, which further affects the calculation result of the remote target, so that the method cannot be ignored, and the detected speed value needs to be corrected to improve the calculation accuracy.

Disclosure of Invention

The invention aims to provide a method for correcting the speed of a long-distance target based on a sawtooth LFMCW waveform system speed measurement radar, which is used for correcting the problem that when the sawtooth LFMCW waveform is used for speed measurement, the long-distance target causes carrier frequency change, so that the calculation result of the long-distance target is influenced.

In order to achieve the purpose, the invention adopts the technical scheme that: a long-distance target speed correction method based on a sawtooth LFMCW waveform system speed measurement radar comprises the following steps:

fast time dimension FFT measures the target distance;

obtaining Doppler frequency shift and long-distance echo frequency shift by slow time dimension FFT;

and correcting the carrier frequency to obtain the speed value of the remote target.

Further, the target distance is:

in the formula: f. of _i For frequency, c is the speed of light, μ is the LFM slope, μ = B/T _e B is bandwidth of frequency modulation, T _e Is a frequency modulation period.

Further, the corrected target speed value is

In the formula: f. of _i Is a frequency f _o Is the original carrier frequency, c is the speed of light, μ is the LFM slope, μ = B/T _e B is bandwidth of frequency modulation, T _e For frequency-modulated period, R ₀ Is the target distance.

The correction method of the invention can fundamentally solve the error generated when the radar slow time dimension FFT is calculated by the linear frequency modulation continuous wave system on the long-distance target and the large frequency modulation slope, has small resource consumption in signal processing, is easy to realize, and can be widely used in the phase-coherent system LFMCW radar.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

Fig. 1 is a diagram illustrating the relationship between the instantaneous frequency of a transmitted signal and time in the prior art.

FIG. 2 is a flow chart of a method for correcting a speed of a remote target according to the present invention.

Fig. 3 is a three-dimensional spectrum diagram of an echo signal obtained according to simulation parameters in an embodiment of the present invention.

Detailed Description

In order to make the implementation objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the embodiments of the present invention.

The actual near and far target echo simulation processes are given below, and the parameters of the simulation processes are described in table 1 below:

table 1 simulation program input parameters

Description of parameters	Unit	State of state	Simulation parameter
				Frequency modulation period T e	S	Input the method	1e-3
Bandwidth B of frequency modulation	Hz	Input the method	1e8
				Target distance R 0	m	Input the method	[1.1e6,5e3,2.5e4]
Target velocity v	m/s	Input the method	[23,7,33]
				Target signal to noise ratio	dB	Input device	[20,15,10]
Carrier frequency f o	Hz	Input device	1e10
				Fast time dimension sampling rate f s	Hz	Input device	2.5e7
Fast time dimension FFT point number Nfft 2		Input device	4096
				FFT point number Nfft in slow time dimension 1		Input device	64

As shown in FIG. 2, the simulation results of the three target range gates can be judged to be [2732,3551,1367] in sequence according to the echo signal-to-noise ratio, and the real distances are [1.1e6,5e3,2.5e4].

Firstly, whether the simulation is correct is verified: unambiguous distance R _u Namely:

R _u ＝c*T _e /2 (9)

wherein, T _e The frequency modulation period, c is the speed of light.

Distance after blur R ₀ Namely:

wherein f is _s For fast time dimension sampling rate, nfft2 is the fast time dimension FFT point number. The three target deblurring back range gates are [2731.8,3551,1366.2 ]]。

Therefore, the simulation result of the range gate is consistent with the calculation result, the simulation result is correct, and the simulation data is available.

The three target speed dimension simulation results are [28,31,14] in sequence, and the real speed is [23,7,33].

Unambiguous velocity V _u Namely:

wherein f is ₀ As carrier frequency, velocity after blurring V ₀ Namely:

wherein, nfft1 is the number of FFT points in the slow time dimension. Carrier frequency in accordance with f ₀ The results of the three targets after removing the non-fuzzy speed are calculated to be 35.13,30.86 and 13.8]. It can be seen that the target is in close range (about kilometer), and the speed is according to the carrier frequency f ₀ The calculation result is basically the same as the simulation value, but the far-distance echo speed and the simulation value are greatly different.

The method of the invention gives out the reason and the solution that the difference between the remote echo speed and the simulation value is large in principle. As can be seen from the previous formula, the slow time dimension echo signal is actually linear frequency modulation, the frequency obtained by actual FFT calculation is broadband, and the center frequency is

The carrier frequency after correction is f ₀ ', i.e.:

the carrier frequency is calculated by adopting the formula, and the results of three targets without fuzzy speed are obtained as 27.4274,30.86 and 13.8, which are basically consistent with the simulation result.

The method can correct the error of the LFMCW speed measurement algorithm of the long-distance echo caused by carrier frequency change, and has important application prospect in practical engineering.

The method can solve the error generated in the calculation of the slow time dimension FFT of the radar of the linear frequency modulation continuous wave system on the long-distance target and the large frequency modulation slope in principle, and compared with the prior art, the method has the following advantages that:

(1) The method is easy to realize in engineering, and the signal processing consumes less resources;

(2) The method of the invention solves the error caused by LFMCW waveform speed measurement in principle;

(3) The method can be widely applied to the phase-coherent system LFMCW radar.

The above description is only for the best mode of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (2)

1. The method for correcting the speed of the long-distance target based on the sawtooth LFMCW waveform system speed measurement radar is characterized by comprising the following steps:

fast time dimension FFT measures the target distance;

obtaining Doppler frequency shift and long-distance echo frequency shift by slow time dimension FFT;

and (3) correcting the carrier frequency to obtain a speed value of the remote target, wherein the relation between the corrected target speed v and the frequency is as follows:

in the formula: f. of _i Is a frequency f _o Is the original carrier frequency, c is the speed of light, μ is the LFM slope, μ = B/T _e B is bandwidth of frequency modulation, T _e For frequency-modulated period, R ₀ Is the target distance.

2. The method for correcting the speed of the long-distance target based on the sawtooth LFMCW waveform system speed radar according to claim 1, wherein the target distance is as follows:

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