Linear frequency modulation distance measurement method, device and system, and storage medium

Abstract

The invention discloses a linear frequency modulation distance measurement method, device and system, and a storage medium. The method comprises the following steps: S1, obtaining a linear frequency modulation signal; and S2, performing time-frequency analysis on the echo signal of the linear frequency modulation signal by using STFT to realize 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

[0001] The present invention belongs to the technical field of signal processing ranging, and in particular relates to a linear frequency modulation ranging method and device, a system, and a storage medium. Background Art

[0002] Linear frequency modulation ranging technology transmits a linear frequency modulation signal (LFM) and uses the characteristic that its frequency changes linearly with time. After being reflected by the target, the echo signal is received, and the wide pulse is compressed into a narrow pulse through pulse compression technology to improve the distance resolution. The target distance is then calculated based on the time delay between the echo signal and the transmitted signal.

[0003] However, this technology has some problems, such as the coupling of distance and Doppler shift may lead to ranging errors, the high sidelobe level of the matched filter will reduce the ability to distinguish multiple small targets, and the hardware performance of the transmitter and receiver limits the signal bandwidth and pulse width, which in turn affects the ranging accuracy. In addition, the complex digital signal processing algorithm places high demands on real-time processing capabilities, and the degree of algorithm optimization directly affects the real-time performance of the system. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a linear frequency modulation ranging method and device, system, and storage medium to solve the problem of poor detection performance of multiple small targets in traditional target detection and recognition technology, and use STFT to perform time-frequency analysis on echo signals, thereby achieving high-precision detection of the distances of multiple small targets.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A linear frequency modulation ranging method, comprising:

[0007] Step S1, obtaining a linear frequency modulation signal;

[0008] Step S2: Use STFT to perform time-frequency analysis on the echo signal of the linear frequency modulation signal to achieve high-precision detection of the distances of multiple small targets.

[0009] 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 using STFT.

[0010] Preferably, in step S2, the mixed intermediate frequency signal is subjected to a short-time Fourier transform STFT, that is:

[0011]

[0012] Where ω(τ-t) is the window function used to localize the signal around time t;

[0013] The signal is divided into multiple short time frames, each frame is N points long, and the window function ω(n) is applied to each frame; the frame signal weighted by the window function is subjected to fast Fourier transform FFT to obtain the spectrum information, and then the spectrum of each frame is arranged in chronological order to generate a time-frequency matrix:

[0014] M(t,f)=|STFT{s IF (t)}(t,ω)| 2

[0015] For each time point t, find the frequency component f with the maximum energy in the frequency f direction on the time-frequency matrix M(t,f). peak ,

[0016] f peak =maxM(t,f)

[0017] By extracting the main frequency f from the time-frequency matrix peak , and the difference between it and the initial frequency f0 can get the frequency offset Δf:

[0018] Δf=f peak (t)-f0

[0019] According to the characteristics of linear frequency modulation signals, the distance and speed information of the target are extracted through frequency difference and Doppler effect. The relationship between the frequency offset Δf=μ*τ caused by the time delay τ and the target distance R is:

[0020]

[0021] Where c is the signal propagation speed and μ is the frequency modulation slope;

[0022] By using different frequency offsets Δf, the distances of different targets can be calculated without distortion.

[0023] The present invention also provides a linear frequency modulation ranging device, comprising:

[0024] An acquisition module, used for acquiring a linear frequency modulation signal;

[0025] The distance measurement module is used to perform time-frequency analysis on the echo signal of the linear frequency modulation signal using STFT to achieve high-precision detection of the distances of multiple small targets.

[0026] Preferably, the ranging module includes:

[0027] A mixing unit, used to mix the received echo signal with the original transmission signal to generate an intermediate frequency signal;

[0028] The analysis unit is used to perform time-frequency analysis on the intermediate frequency signal using STFT.

[0029] Preferably, the analysis unit is used to calculate the distances of different targets based on the frequency component with the maximum energy in the frequency f direction on the time-frequency matrix and the frequency offset.

[0030] The present invention also provides a linear frequency modulation ranging system, comprising: a memory and a processor, wherein the memory stores a computer program to be run by the processor, and the computer program executes the linear frequency modulation ranging method when being run by the processor.

[0031] The present invention also provides a storage medium, on which a computer program is stored, and the computer program executes the linear frequency modulation ranging method when running.

[0032] The STFT-based LFM ranging technology of the present invention introduces a time-frequency joint analysis method to process and analyze the echo signal in more detail, which has the following technical effects:

[0033] 1. Stronger multi-target resolution capability: STFT can perform time-frequency analysis on signals, expand the echo signal into two dimensions: time and frequency. By observing the time-frequency diagram, the frequency change trajectories corresponding to multiple targets can be clearly distinguished, thus improving the target resolution capability.

[0034] 2. Ability to adapt to complex environments (multipath effect): The time-frequency joint representation of STFT can separate echo signals of different paths. By analyzing the time-frequency characteristics of each signal, the main path information of the target can be extracted, effectively reducing the impact of multipath interference on the ranging results.

[0035] 3. Improve the processing capability of non-stationary signals: STFT can analyze the instantaneous spectrum under non-stationary signal conditions and capture the rapid changes of signals through dynamic time-frequency analysis. It is suitable for processing non-stationary echo signals, especially when the target state changes rapidly.

[0036] 4. Improve anti-noise performance: STFT performs energy-concentrated analysis of the signal through a local time-frequency window, which can highlight the characteristics of the target signal under a strong noise background and significantly improve the anti-noise performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0038] Figure 1 This is a flow chart of the linear frequency modulation ranging method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Embodiment 1:

[0042] like Figure 1 As shown, an embodiment of the present invention provides a linear frequency modulation ranging method, which performs LFM ranging based on STFT, separates signals by adding different window functions, and accurately identifies multiple targets with extremely close intervals and easy signal aliasing without generating aliasing, including:

[0043] Step S1: System initialization

[0044] At the beginning of the system startup, each key module needs to be initialized in turn. First, start the signal transmission module so that it can stably send out signals for ranging; then, activate the signal receiving module to ensure that it has the ability to accurately capture signals; at the same time, turn on the signal processing module to effectively analyze and process the received signals; in addition, start the data processing and control module to provide support for subsequent data calculations and equipment control; the communication module also needs to be started synchronously to ensure the smooth transmission of information inside and outside the system; finally, turn on the power module to provide a stable energy supply for the operation of the entire system. Through this series of initialization processes, a comprehensive check and ensure that each module is in normal working condition, laying the foundation for subsequent accurate ranging.

[0045] After the module is initialized, the system calibration phase begins. An area with a known precise distance is selected as the calibration site, and the system is calibrated for ranging accuracy using the site. By comparing the difference between the distance measured by the system and the actual known distance, fine-tuning the system's internal parameter settings, algorithm logic, etc. is performed to effectively eliminate measurement deviations caused by factors such as equipment errors and environmental interference. During the calibration process, special attention should be paid to the impact of the equipment's system errors and environmental factors on the signal, and system parameters such as transmit power and receive sensitivity should be adjusted according to the actual measured values ​​to ensure system accuracy.

[0046] Step S2: Signal transmission

[0047] Generate a linear frequency modulated signal (LFM) whose frequency changes linearly with time. The generation of this signal can be described by a mathematical expression. Assuming the initial frequency of the LFM signal is f0 and the frequency change rate (frequency modulation slope) is β, the instantaneous frequency f(t) of the LFM signal can be expressed as:

[0048] f(t)=f0+β*t

[0049] The time domain expression of LFM (linear frequency modulation) signal is:

[0050]

[0051] in, represents a rectangular pulse with a width of τ, which is used to limit the duration of the signal; f0 is the center frequency of the signal; μ is the frequency modulation slope, defined as B is the bandwidth of the signal, which is the pulse width of the signal; t is the time variable.

[0052] The phase of this signal changes linearly with time and consists of two parts: one is the phase 2πf generated by the carrier frequency f0 o t, and the other part is the phase πβt generated by the frequency modulation slope β 2 .

[0053] The generated linear frequency modulation (LFM) signal needs to be 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 different copies of the spectrum of the sampled signal do not overlap, thereby ensuring that the signal can be completely restored through the bandpass filter.

[0054] For LFM signal, the highest frequency is:

[0055] f max =f0+K*t

[0056] Where T is the duration of the signal. Therefore, the sampling frequency should satisfy:

[0057] f s ≥2*f max =2*(f0+K*t)

[0058] Step S3: Signal reception

[0059] Receive signal: Receive linear frequency modulation signal:

[0060]

[0061] Where τ is the delay of the target signal is the target distance, c is the wave speed.

[0062] Mixing process: The received echo signal is mixed with the original transmitted signal to generate an intermediate frequency (IF) signal. The frequency of the mixed signal is the frequency difference between the echo signal and the transmitted signal, which reflects the relative motion of the target:

[0063] S IF (t) = s(t)*r(t)

[0064] The mixed IF signal can be used for further analysis.

[0065] Step S4: Signal processing

[0066] Perform short-time Fourier transform (STFT) on the mixed intermediate frequency signal: Perform short-time Fourier transform on the received signal to obtain the local information of the signal in the time-frequency domain. The definition of STFT is:

[0067]

[0068] Where ω(τ-t) is a window function used to localize the signal around time t.

[0069] Parameter settings:

[0070] Window function: Select an appropriate window function (such as Hanning window, Hamming window, etc.) to balance the time-frequency resolution.

[0071] Frame length and frame shift: Set the appropriate frame length and frame shift to control the resolution of time and frequency. The longer the frame length, the higher the frequency resolution; the smaller the frame shift, the higher the time resolution.

[0072] In order to construct the time-frequency matrix, the signal needs to be divided into multiple short time frames, each frame length is N points, and the window function ω(n) is applied to each frame. The frame signal weighted by the window function is subjected to fast Fourier transform (FFT) to obtain the spectrum information, and then the spectrum of each frame is arranged in time order to generate the time-frequency matrix:

[0073] M(t,f)=|STFT{s IF (t)}(t,ω)| 2 .

[0074] The horizontal axis of the matrix represents time, and the vertical axis represents frequency. The distribution of energy in the matrix can intuitively reflect the characteristics of the target signal.

[0075] STFT allows the frequency components of the signal to be analyzed at each time point t, so that information in the time domain and frequency domain can be obtained simultaneously. This local analysis is particularly suitable for non-stationary signals whose frequency changes with time, and is particularly important in ranging systems, especially when the reflected signal of the target is frequency modulated (such as linear frequency modulation LFM signal), FFT cannot directly display the characteristics of frequency changing with time. Therefore, it has the ability to accurately separate multiple targets and the ability to identify targets at close range that the fast Fourier transform does not have.

[0076] Step S5: Time-frequency analysis

[0077] STFT limits the length of the signal analyzed each time through the window function, and its computational complexity is controlled to a certain extent. STFT can ensure real-time performance through fast algorithms (such as fast Fourier transform combined with sliding window). At the same time, STFT can smoothly observe the frequency changes of the signal during the window sliding process, while FFT cannot provide such local smooth analysis. For dynamically changing signals, STFT can better track subtle changes in frequency and avoid distortion or inaccuracy caused by global spectrum analysis.

[0078] For each time point t, we can find the frequency component f with the maximum energy in the frequency f direction on the time-frequency matrix M(t,f) peak :

[0079] f peak =maxM(t,f)

[0080] This represents the main frequency of the echo signal at that moment. If there are multiple echo signals, there are multiple main frequencies.

[0081] The target frequency offset Δf reflects the change in the echo signal frequency. The main frequency f extracted from the time-frequency matrix peak , and the difference between it and the initial frequency f0 can get the frequency offset Δf:

[0082] Δf=f peak (t)-f0

[0083] Subsequently, according to the characteristics of the linear frequency modulation signal, the distance and speed information of the target can be extracted through the frequency difference and the Doppler effect. The relationship between the frequency offset Δf = μ*τ caused by the time delay τ and the target distance R is:

[0084]

[0085] By using different frequency offsets Δf, the distances of different targets can be calculated without distortion. c is the signal propagation speed and μ is the frequency modulation slope.

[0086] STFT can divide the signal into suitable short time periods, and perform Fourier transform in each time period, thereby providing local information of the signal in time and frequency at the same time. By analyzing the local information, the frequency analysis of signals with very close intervals can be separated without distortion through different function windows in the frequency domain, and then the position information of multiple targets can be detected. Compared with the traditional Fourier transform that can only perform global signal analysis, this time-frequency localized analysis can more accurately capture the local transient changes and time-varying characteristics of the signal, which is helpful to achieve accurate ranging of multiple small targets in a complex signal environment. The present invention will solve the limitations of the prior art in positioning and sonar detection by detecting and identifying targets through linear frequency modulation (LFM) ranging technology based on short-time Fourier transform (STFT), and provide a new technical means for detecting and identifying targets.

[0087] Embodiment 2:

[0088] The embodiment of the present invention further provides a linear frequency modulation ranging device, comprising:

[0089] An acquisition module, used for acquiring a linear frequency modulation signal;

[0090] The distance measurement module is used to perform time-frequency analysis on the echo signal of the linear frequency modulation signal using STFT to achieve high-precision detection of the distances of multiple small targets.

[0091] As an implementation manner of the embodiment of the present invention, the ranging module includes:

[0092] A mixing unit, used to mix the received echo signal with the original transmission signal to generate an intermediate frequency signal;

[0093] The analysis unit is used to perform time-frequency analysis on the intermediate frequency signal using STFT.

[0094] As an implementation manner of an embodiment of the present invention, the analysis unit is used to calculate the distances of different targets based on the frequency component with the maximum energy in the frequency f direction on the time-frequency matrix and the frequency offset.

[0095] Embodiment 3:

[0096] An embodiment of the present invention further provides a linear frequency modulation ranging system, comprising: a memory and a processor, wherein the memory stores a computer program executed by the processor, and the computer program executes the linear frequency modulation ranging method when executed by the processor.

[0097] Embodiment 3:

[0098] An embodiment of the present invention further provides a storage medium, on which a computer program is stored, and the computer program executes the linear frequency modulation ranging method when running.

[0099] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A linear frequency modulation ranging method, characterized in that: include: Step S1, obtaining a linear frequency modulation signal; Step S2: Use STFT to perform time-frequency analysis on the echo signal of the linear frequency modulation signal to achieve high-precision detection of the distances of multiple small targets.

2. The linear frequency modulation ranging method according to claim 1, characterized in that: 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 using STFT.

3. The linear frequency modulation ranging method according to claim 2, characterized in that: In step S2, the mixed intermediate frequency signal is subjected to a short-time Fourier transform STFT, namely: Where ω(τ-t) is the window function used to localize the signal around time t; The signal is divided into multiple short time frames, each frame is N points long, and the window function ω(n) is applied to each frame; the frame signal weighted by the window function is subjected to fast Fourier transform FFT to obtain the spectrum information, and then the spectrum of each frame is arranged in chronological order to generate a time-frequency matrix: M(t,f)=|STFT{s IF (t)}(t,ω)| 2 For each time point t, find the frequency component f with the maximum energy in the frequency f direction on the time-frequency matrix M(t,f). peak , f peak =maxM(t,f) By extracting the main frequency f from the time-frequency matrix peak , and make a difference with the initial frequency f0 to get the frequency offset Δf: Δf=f peak (t)-f0 According to the characteristics of linear frequency modulation signals, the distance and speed information of the target are extracted through frequency difference and Doppler effect. The relationship between the frequency offset Δf=μ*τ caused by the time delay τ and the target distance R is: Where c is the signal propagation speed and μ is the frequency modulation slope; By using different frequency offsets Δf, the distances of different targets can be calculated without distortion.

4. A linear frequency modulation ranging device, characterized in that: include: An acquisition module, used for acquiring a linear frequency modulation signal; The distance measurement module is used to perform time-frequency analysis on the echo signal of the linear frequency modulation signal using STFT to achieve high-precision detection of the distances of multiple small targets.

5. The linear frequency modulation ranging device as claimed in claim 4, characterized in that: The ranging module includes: A mixing unit, used to mix the received echo signal with the original transmission signal to generate an intermediate frequency signal; The analysis unit is used to perform time-frequency analysis on the intermediate frequency signal using STFT.

6. The linear frequency modulation distance measuring device as claimed in claim 5, characterized in that: The analysis unit is used to calculate the distances of different targets based on the frequency component with the maximum energy in the frequency f direction on the time-frequency matrix and the frequency offset.

7. A linear frequency modulation ranging system, characterized in that: include: A memory and a processor, wherein the memory stores a computer program executed by the processor, and when the computer program is executed by the processor, the linear frequency modulation ranging method according to any one of claims 1 to 3 is executed.

8. A storage medium, characterized in that: The storage medium stores a computer program, and the computer program executes the linear frequency modulation ranging method according to any one of claims 1 to 3 when running.

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