CN119689454A - A linear frequency modulation ranging method, device, system and storage medium - Google Patents
A linear frequency modulation ranging method, device, system and storage medium Download PDFInfo
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Abstract
The invention discloses a linear frequency modulation ranging method, a linear frequency modulation ranging device, a linear frequency modulation ranging system and a storage medium, wherein the linear frequency modulation ranging method comprises the following steps of S1, obtaining a linear frequency modulation signal; and S2, performing time-frequency analysis on echo signals of the linear frequency modulation signals by using STFT, and realizing high-precision detection of a plurality of small target distances. By adopting the technical scheme of the invention, the problem of poor detection performance of a plurality of small targets in the traditional target detection and identification technology is solved.
Description
Technical Field
The invention belongs to the technical field of signal processing ranging, and particularly relates to a linear frequency modulation ranging method, a linear frequency modulation ranging device, a linear frequency modulation ranging system and a storage medium.
Background
The linear frequency modulation ranging technology is to transmit a linear frequency modulation signal (LFM), receive an echo signal after being reflected by a target by utilizing the characteristic that the frequency of the linear frequency modulation signal (LFM) changes linearly along with time, compress a wide pulse into a narrow pulse by a pulse compression technology to improve the distance resolution, and calculate the target distance according to the time delay between the echo signal and the transmitted signal.
However, this technique has problems such as coupling of range and doppler shift may cause ranging errors, high side lobe levels of the matched filter may reduce resolution of multiple small targets, and hardware performance of the transmitter and receiver limits signal bandwidth and pulse width, which in turn affects ranging accuracy. In addition, the complex digital signal processing algorithm has higher requirements on the real-time processing capacity, and the optimization degree of the algorithm directly influences the real-time performance of the system.
Disclosure of Invention
The invention aims to solve the technical problem of providing a linear frequency modulation ranging method, a linear frequency modulation ranging device, a linear frequency modulation ranging system and a storage medium, solving the problem of poor detection performance of a plurality of small targets in the traditional target detection and identification technology, and performing time-frequency analysis on echo signals by using STFT so as to realize high-precision detection of the plurality of small target distances.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a chirped ranging method comprising:
S1, obtaining a linear frequency modulation signal;
And S2, performing time-frequency analysis on echo signals of the linear frequency modulation signals by using STFT, and realizing high-precision detection of a plurality of small target distances.
Preferably, in step S2, the received echo signal is mixed with the original transmission signal to generate an intermediate frequency signal, and the intermediate frequency signal is subjected to time-frequency analysis by STFT.
Preferably, in step S2, the mixed intermediate frequency signal is subjected to short-time fourier transform STFT, that is:
where ω (τ -t) is a window function for localizing the signal around time t;
Dividing the signal into a plurality of short time frames, wherein the length of each frame is N points, and applying a window function omega (N) on each frame:
M(t,f)=|STFT{sIF(t)}(t,ω)|2
For each time point t, find the frequency component f peak with the largest energy in the frequency f direction on the time-frequency matrix M (t, f),
fpeak=maxM(t,f)
The frequency offset Δf can be obtained by making a difference between the primary frequency f peak extracted from the time-frequency matrix and the initial frequency f 0:
Δf=fpeak(t)-f0
According to characteristics of the linear frequency modulation signal, distance and speed information of a target are extracted through a frequency difference and a Doppler effect, and the relation between the frequency offset delta f=mu=tau and the distance R of the target, which is caused by the time delay tau, is as follows:
Where c is the signal propagation speed and μ is the frequency modulation slope;
by means of the different frequency offsets Δf, distances of different targets can be calculated undistorted.
The invention also provides a linear frequency modulation distance measuring device, which comprises:
the acquisition module is used for acquiring the linear frequency modulation signal;
and the ranging module is used for carrying out time-frequency analysis on echo signals of the linear frequency modulation signals by using STFT so as to realize high-precision detection of a plurality of small target distances.
Preferably, the ranging module includes:
The frequency mixing unit is used for mixing the received echo signal with the original transmitting signal to generate an intermediate frequency signal;
and the analysis unit is used for carrying out time-frequency analysis on the intermediate frequency signal by using STFT.
Preferably, the analysis unit is configured to calculate the distances between different targets according to the frequency component and the frequency offset with the largest energy in the frequency f direction on the time-frequency matrix.
The invention also provides a linear frequency modulation ranging system which comprises a memory and a processor, wherein the memory is stored with a computer program operated by the processor, and the computer program executes a linear frequency modulation ranging method when being operated by the processor.
The present invention also provides a storage medium having stored thereon a computer program that, when run, performs a chirped ranging method.
The STFT-based LFM ranging technology introduces a time-frequency joint analysis mode, carries out finer processing and analysis on echo signals, and has the following technical effects:
1. The method has stronger multi-target resolution capability, namely the STFT can perform time-frequency analysis on the signals, expand echo signals to two dimensions of time and frequency, and can clearly resolve frequency change tracks corresponding to a plurality of targets by observing a time-frequency diagram, thereby improving the resolution capability of the targets.
2. The capability of adapting to complex environments (multipath effects) is that the time-frequency joint characterization of STFT can separate echo signals of different paths, and the influence of multipath interference on a ranging result is effectively reduced by analyzing the time-frequency characteristic of each path of signal and extracting the main path information of a target.
3. The STFT can analyze the instantaneous frequency spectrum under the condition of the non-stationary signal, captures the rapid change of the signal through dynamic time-frequency analysis, is suitable for processing the non-stationary echo signal, and particularly has better performance under the condition of rapid change of the target state.
4. The anti-noise performance is improved, namely the STFT performs energy centralized analysis on the signal through a local time-frequency window, so that the characteristic of the target signal can be highlighted under a strong noise background, and the anti-noise performance is remarkably improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a chirp ranging method according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1:
As shown in fig. 1, an embodiment of the present invention provides a linear frequency modulation ranging method, performing LFM ranging based on STFT, performing signal separation by adding different window functions, and accurately identifying a plurality of targets with very close intervals and easily aliased signals without generating aliases, including:
Step S1, initializing the system
At the beginning of system start, each key module needs to be initialized in turn. The method comprises the steps of starting a signal transmitting module to enable the signal transmitting module to stably send out signals for ranging, activating a signal receiving module to ensure that the signal receiving module has the capability of accurately capturing signals, starting a signal processing module to effectively analyze and process the received signals, starting a data processing and control module to support subsequent data operation and equipment control, synchronously starting a communication module to ensure smooth transmission of internal and external information of a system, and finally switching on a power module to provide stable energy supply for operation of the whole system. Through the series of initialization processes, all modules are comprehensively checked and ensured to be in a normal working state, and a foundation is laid for the follow-up accurate ranging.
After the initialization of the module is completed, a system calibration stage is entered. And selecting a section of region with known accurate distance as a calibration field, and calibrating the ranging accuracy of the system by using the field. By comparing the difference between the measured distance and the actual known distance of the system, the parameter setting, the algorithm logic and the like in the system are finely adjusted, so that measurement deviation caused by factors such as equipment errors, environmental interference and the like is effectively eliminated. Special attention should be paid to the influence of the system error of the device and environmental factors on the signal during the calibration process, and system parameters such as transmit power, receive sensitivity, etc. are adjusted according to the actual measured values to ensure the accuracy of the system.
Step S2, signal transmission
A chirp signal (LFM) is generated whose frequency varies linearly with time. The generation of such a signal can be described by a mathematical expression. Assuming that the initial frequency of the LFM signal is f 0 and the frequency change rate (frequency modulation slope) is β, the instantaneous frequency f (t) of the LFM signal can be expressed as:
f(t)=f0+β*t
the time domain expression of LFM (linear frequency modulation) signals is:
wherein, A rectangular pulse of width τ is used to limit the duration of the signal, f 0 is the center frequency of the signal, μ is the frequency modulation slope, defined asB is the bandwidth of the signal, is the pulse width of the signal, and t is the time variable.
The phase of this signal varies linearly with time and consists of one part of the phase 2 pi f o t generated by carrier frequency f 0 and the other part of the phase pi beta t 2 generated by the frequency modulation slope beta.
The resulting chirped signal (LFM) is digitally sampled for subsequent digital signal processing and transmission. According to the nyquist sampling theorem, the sampling frequency fs must be at least twice the highest frequency component of the signal to avoid aliasing. This condition ensures that there is no overlap between the different copies of the spectrum of the sampled signal, thereby ensuring that the signal is completely restored by the bandpass filter.
For LFM signals, the highest frequencies are:
fmax＝f0+K*t
where T is the duration of the signal. Therefore, the sampling frequency should satisfy:
fs≥2*fmax＝2*(f0+K*t)
step S3, signal reception
Receiving signals, namely receiving linear frequency modulation signals:
where τ is the delay of the target signal For the target distance, c is the wave velocity.
Mixing processing, namely mixing the received echo signal with the original transmission signal to generate an Intermediate Frequency (IF) signal. The mixed signal frequency is the frequency difference between the echo signal and the transmit signal, which reflects the relative motion of the target:
SIF(t)=s(t)*r(t)
the mixed intermediate frequency signal can be used for further analysis.
Step S4 signal processing
Short-time Fourier transform (STFT) is performed on the mixed intermediate frequency signals, namely, the received signals are subjected to short-time Fourier transform so as to acquire local information of the signals in a time-frequency domain. The definition of STFT is:
where ω (τ -t) is a window function for localizing the signal around time t.
Parameter setting:
Window function-a suitable window function (e.g., hanning window, hamming window, etc.) is selected to balance time-frequency resolution.
Frame length and frame shift-the proper frame length and frame shift are set to control the resolution of time and frequency. The longer the frame length, the higher the frequency resolution, and the smaller the frame shift, the higher the time resolution.
To construct the time-frequency matrix, the signal is divided into a number of short time frames, each frame being N points in length, and a window function ω (N) is applied over each frame. Performing Fast Fourier Transform (FFT) on the frame signals weighted by the window function to obtain spectrum information, and then arranging the spectrums of the frames in time sequence to generate a time-frequency matrix:
M(t,f)=|STFT{sIF(t)}(t,ω)|2。
The horizontal axis of the matrix represents time, the vertical axis represents frequency, and the distribution of energy in the matrix can intuitively reflect the characteristics of a target signal.
The STFT allows the frequency components of the signal to be analyzed at each point in time t, so that information of the time domain and the frequency domain can be obtained simultaneously. Such local analysis is particularly suitable for non-stationary signals whose frequency varies with time, and is particularly important in ranging systems, especially when the reflected signal of the target is frequency modulated (e.g., a chirped LFM signal), where the FFT cannot directly show the frequency-varying characteristics. He therefore has the ability to precisely separate multiple objects that the fast fourier transform does not possess and the ability to identify objects at close range.
Step S5, time-frequency analysis
STFT limits the signal length of each analysis by a window function, whose computational complexity is controlled to some extent. STFT can guarantee real-time by a fast algorithm (e.g., fast fourier transform combined with sliding window). Meanwhile, the STFT can smoothly observe the frequency variation of the signal during the window sliding, and the FFT cannot provide such a local smooth analysis. For dynamically varying signals, the STFT is able to better track small changes in frequency, avoiding distortion or inaccuracy due to global spectral analysis.
For each time point t, we can find the frequency component f peak with the greatest energy in the frequency f direction on the time-frequency matrix M (t, f):
fpeak=maxM(t,f)
This represents the dominant frequency of the echo signal at that time, and there are multiple dominant frequencies for the echo signal.
The frequency offset deltaf of the target reflects the change in the echo signal frequency. The frequency offset Δf can be obtained by making a difference between the primary frequency f peak extracted from the time-frequency matrix and the initial frequency f 0:
Δf=fpeak(t)-f0
Distance and velocity information of the target can then be extracted by frequency difference and doppler effect, depending on the characteristics of the chirp signal. The frequency offset Δf=μ×τ due to the delay τ is related to the target distance R as follows:
with different frequency offsets Δf, distances of different targets can be calculated undistorted, c is the signal propagation speed, and μ is the chirp rate.
The STFT can divide the signal into suitable short time periods and perform Fourier transformation in each time period, so that local information of the signal in time and frequency is provided at the same time, through analysis of the local information, the frequency analysis of the signal with extremely close intervals can be separated out through different function windows in a frequency domain, so that the position information of multiple targets can be detected, and compared with the traditional Fourier transformation which can only perform global signal analysis, the time-frequency localization analysis can capture local transient changes and time-varying characteristics of the signal more accurately, and is beneficial to realizing accurate ranging of multiple small targets in a complex signal environment. The invention solves the limitation of the prior art in positioning and sonar detection by the target detection and identification based on the Linear Frequency Modulation (LFM) ranging technology of short-time Fourier transform (STFT), and provides a new technical means for the detection and identification of targets.
Example 2:
the embodiment of the invention also provides a linear frequency modulation ranging device, which comprises:
the acquisition module is used for acquiring the linear frequency modulation signal;
and the ranging module is used for carrying out time-frequency analysis on echo signals of the linear frequency modulation signals by using STFT so as to realize high-precision detection of a plurality of small target distances.
As one implementation of the embodiment of the present invention, the ranging module includes:
The frequency mixing unit is used for mixing the received echo signal with the original transmitting signal to generate an intermediate frequency signal;
and the analysis unit is used for carrying out time-frequency analysis on the intermediate frequency signal by using STFT.
As an implementation manner of the embodiment of the present invention, the analysis unit is configured to calculate the distances between different targets according to the frequency component and the frequency offset with the largest energy in the frequency f direction on the time-frequency matrix.
Example 3:
The embodiment of the invention also provides a linear frequency modulation ranging system which comprises a memory and a processor, wherein the memory is stored with a computer program operated by the processor, and the computer program executes a linear frequency modulation ranging method when being operated by the processor.
Example 3:
the embodiment of the invention also provides a storage medium, and a computer program is stored on the storage medium, and the computer program executes the linear frequency modulation ranging method when running.
The above embodiments are merely illustrative of the preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but various modifications and improvements made by those skilled in the art to which the present invention pertains are made without departing from the spirit of the present invention, and all modifications and improvements fall within the scope of the present invention as defined in the appended claims.
Claims (8)
1. A method of chirping ranging comprising:
S1, obtaining a linear frequency modulation signal;
And S2, performing time-frequency analysis on echo signals of the linear frequency modulation signals by using STFT, and realizing high-precision detection of a plurality of small target distances.
2. The method of claim 1, wherein in step S2, the received echo signal is mixed with the original transmission signal to generate an intermediate frequency signal, and the intermediate frequency signal is subjected to time-frequency analysis by STFT.
3. The chirped ranging method as claimed in claim 2, wherein in step S2, short-time fourier transform STFT is performed on the mixed intermediate frequency signal, namely:
where ω (τ -t) is a window function for localizing the signal around time t;
Dividing the signal into a plurality of short time frames, wherein the length of each frame is N points, and applying a window function omega (N) on each frame:
M(t,f)=|STFT{sIF(t)}(t,ω)|2
For each time point t, find the frequency component f peak with the largest energy in the frequency f direction on the time-frequency matrix M (t, f),
fpeak=maxM(t,f)
The frequency offset Δf is obtained by making a difference between the primary frequency f peak extracted from the time-frequency matrix and the initial frequency f 0:
Δf=fpeak(t)-f0
According to characteristics of the linear frequency modulation signal, distance and speed information of a target are extracted through a frequency difference and a Doppler effect, and the relation between the frequency offset delta f=mu=tau and the distance R of the target, which is caused by the time delay tau, is as follows:
Where c is the signal propagation speed and μ is the frequency modulation slope;
by means of the different frequency offsets Δf, distances of different targets can be calculated undistorted.
4. A chirped distance measurement device, comprising:
the acquisition module is used for acquiring the linear frequency modulation signal;
and the ranging module is used for carrying out time-frequency analysis on echo signals of the linear frequency modulation signals by using STFT so as to realize high-precision detection of a plurality of small target distances.
5. The chirped ranging apparatus of claim 4 wherein the ranging module comprises:
The frequency mixing unit is used for mixing the received echo signal with the original transmitting signal to generate an intermediate frequency signal;
and the analysis unit is used for carrying out time-frequency analysis on the intermediate frequency signal by using STFT.
6. The chirped distance measurement device of claim 5 wherein the analysis unit is configured to calculate distances of different targets based on a frequency component and a frequency offset with a maximum energy in a frequency f direction on the time-frequency matrix.
7. A chirped ranging system comprising a memory and a processor, the memory having stored thereon a computer program for execution by the processor, the computer program when executed by the processor performing the chirped ranging method of any of claims 1-3.
8. A storage medium having stored thereon a computer program which, when run, performs the chirped ranging method of any of claims 1-3.
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