CN-115561486-B - Laser Doppler frequency spectrum correction method based on power spectrum analysis

Abstract

The invention discloses a dynamic laser Doppler frequency spectrum correction method, which only carries out inhibition treatment on fixed position noise of a frequency spectrum, and because Doppler frequency spectrum noise positions corresponding to different laser velocimetry systems are not necessarily the same, the method has no universality, has poor inhibition effect, still has unstable frequency spectrum noise phenomenon and causes interference to frequency spectrum calculation of the velocimetry systems, thereby providing the laser Doppler frequency spectrum correction method based on power spectrum analysis. The method is used for signal suppression based on power spectrum analysis, has good universality, obvious spectrum noise suppression effect and stable spectrum noise, and lays a foundation for accurately extracting Doppler signals in subsequent spectrum calculation.

Inventors

• Chong Zehui
• XU YONGQIANG
• YANG SHOUBO
• LIU PAN
• YUAN YANHUA

Assignees

• 北京控制与电子技术研究所

Dates

Publication Date

20260508

Application Date

20220826

Claims (3)

1. 1. A laser Doppler spectrum noise suppression method based on power spectrum analysis is characterized by comprising the following specific steps: first step, a laser Doppler spectrum processing system based on power spectrum analysis is built The laser Doppler spectrum processing system based on the power spectrum analysis comprises a spectrum acquisition module and a spectrum processing module; the second step of the spectrum acquisition module acquires Doppler signal power spectrum The frequency spectrum acquisition module converts the laser Doppler signal acquired by the photoelectric detector into a photocurrent signal, and then converts the analog quantity signal into a digital quantity time domain Doppler signal through pre-amplification filtering; The core of laser speed measurement is to find out the frequency value corresponding to the highest frequency point in the power spectrum, and calculate the speed value according to the frequency value; The third step of the spectrum processing module extracts static power spectrum background noise The Doppler signal power spectrum not only contains Doppler effective signals detected by the laser velocimeter, but also is mixed with noise signals caused by circuit noise, and the noise signals are randomly distributed at each frequency point position of the power spectrum; when the circuit noise is not suppressed, once the circuit noise signal amplitude exceeds the effective Doppler signal amplitude, the noise signal is misjudged as an effective signal so as to calculate an error speed value; The noise signals are randomly distributed at all frequency points of the power spectrum, the envelope shape of the noise signals in the power spectrum is not changed, the spectrum processing module extracts the envelope of the noise signals according to the distribution characteristics of the noise signals, no Doppler signals are output in the static placement process of the velocimeter, the power spectrum only contains circuit noise information, so 400 frames of power spectrums are collected as samples, each frame of power spectrum consists of 8192 frequency points, and the average amplitude of each frequency point of the power spectrum is calculated and is represented by a formula (1): Wherein F i represents the power spectrum of the ith frame, the obtained average power spectrum can reflect the envelope distribution of circuit noise, and the envelope distribution is taken as background noise; the fourth step of the spectrum processing module performs static power spectrum base noise analysis The spectrum processing module collects 400 frames of static power spectrum background noise and analyzes the base noise of the power spectrum, and the base noise is expressed by a formula (2): The base noise is used for calculating the signal-to-noise ratio later; Fifth step, the spectrum processing module analyzes the power spectrum signal-to-noise ratio The spectrum processing module determines the signal to noise ratio of the power spectrum of the velocimeter and is expressed by a formula (3): In the formula (3), F is the current acquired power spectrum, and the signal-to-noise ratio Q represents the intensity of the highest peak frequency in the current acquired power spectrum; When the laser velocimeter is placed at rest, the velocimeter does not feel effective Doppler signals, the signal to noise ratio Q is stably kept below 100, and the velocimeter is not interfered by circuit noise; When the laser velocimeter moves along with the carrier, the velocimeter can be sensitive to an effective Doppler signal, the effective Doppler signal appears as an obvious spike signal in the whole power spectrum, the signal-to-noise ratio Q of the spike signal is usually more than 1000, and the speed can be accurately calculated according to the position of the spike in the power spectrum; the sixth step of the frequency spectrum processing module carries out dynamic updating of background noise and base noise The collected 400 frames of background noise and base noise can reflect the envelope shape of the power spectrum, but as the use time is accumulated, the circuit hardware temperature can be changed, the envelope shape of the power spectrum can be affected to a certain extent, and the spectrum processing module dynamically updates the background noise and the base noise in real time; The update of the background noise is expressed by formula (4): F ave ＝k·F ave1 +(1-k)·F ave2 (4) In the formula (4), F ave is updated background noise, F ave1 is historical background noise, F ave2 is background noise of the current frame, k is a weight coefficient, and since the change of each frame of the power spectrum envelope is very tiny, the weight coefficient takes k=0.9995; the update of the base noise is expressed by formula (5): In the formula (5), F sqr is updated background noise, F sqr1 is historical background noise, F ave1 is historical background noise, F is doppler spectrum of the current frame, k is a weight coefficient, and k=0.9995 is taken as the weight coefficient; thus, the laser Doppler spectrum correction based on the power spectrum analysis is completed.
2. 2. The laser Doppler spectrum noise suppression method based on power spectrum analysis according to claim 1, wherein the spectrum acquisition module is characterized by realizing the acquisition of high-precision Doppler frequency domain signals, and storing digital Doppler signals obtained by A/D conversion into a first-in first-out FIFO unit in the system through an FPGA chip for use by a spectrum processing module.
3. 3. The method for suppressing laser Doppler spectrum noise based on power spectrum analysis as claimed in claim 1, wherein the spectrum processing module has the functions of taking ARM chip STM32H743 as a core, transmitting spectrum signals to the ARM chip through a first-in first-out FIFO unit through time sequence control, then performing spectrum noise correction processing on Doppler signal power spectrum, extracting power spectrum background noise and performing suppression processing.

Description

Laser Doppler frequency spectrum correction method based on power spectrum analysis Technical Field The invention relates to a laser Doppler frequency spectrum correction method, in particular to a laser Doppler frequency spectrum correction method based on power spectrum analysis. Background Compared with an odometer, the laser Doppler velocimeter Laser Doppler Velocimeter belongs to non-contact measuring equipment, realizes high-precision measurement of the maneuvering speed of the vehicle carrier by utilizing the Doppler effect of laser, can isolate adverse effects of factors such as tire pressure change, maneuvering in a turning, skidding and the like of the vehicle carrier, is one of effective ways for solving the problem of high-precision autonomous positioning adaptability of the vehicle carrier, and has the outstanding advantages of high response speed, high spatial resolution, large measuring range and the like. The accurate extraction of the laser Doppler frequency signal is important in engineering practice for realizing high-precision laser speed measurement, and the precision of speed measurement is directly influenced. However, due to the interference of circuit noise factors, the accurate calculation of signals is generally affected, and when serious, the error speed is calculated and output to positioning and orientation equipment, so that the positioning error is increased. Disclosure of Invention The invention aims to provide a laser Doppler spectrum correction method based on power spectrum analysis, which solves the problem of unstable laser Doppler spectrum noise. The laser Doppler spectrum noise suppression method based on the power spectrum analysis comprises the following specific steps: first step, a laser Doppler spectrum processing system based on power spectrum analysis is built The laser Doppler spectrum processing system based on the power spectrum analysis comprises a spectrum acquisition module and a spectrum processing module. The frequency spectrum acquisition module has the functions of realizing the acquisition of high-precision Doppler frequency domain signals, and storing digital Doppler storage signals obtained by A/D conversion into a first-in first-out FIFO unit in the system through the FPGA chip for the frequency spectrum processing module to use. The spectrum processing module has the functions that an ARM chip STM32H743 is used as a core, a first-in first-out FIFO unit transmits spectrum signals to the ARM chip through time sequence control, then spectrum noise correction processing is carried out on Doppler signal power spectrums, power spectrum background noise is extracted, and suppression processing is carried out. The second step of the spectrum acquisition module acquires Doppler signal power spectrum The spectrum acquisition module converts the laser Doppler signals acquired by the photoelectric detector into photocurrent signals, and then the photocurrent signals are subjected to pre-amplification filtering, and finally the analog quantity signals are converted into digital quantity time domain Doppler signals. The detected time domain Doppler signals are converted into frequency spectrums through the FPGA chip by fast Fourier transform FFT, and the frequency spectrums are power spectrums of the Doppler signals. The core of the laser speed measurement is to find out the frequency value corresponding to the highest frequency point in the power spectrum, and calculate the speed value according to the frequency value. The third step of the spectrum processing module extracts static power spectrum background noise The Doppler signal power spectrum not only contains Doppler effective signals detected by the laser velocimeter, but also is mixed with noise signals caused by circuit noise, and the noise signals are randomly distributed at each frequency point position of the power spectrum. When the circuit noise is not suppressed, once the circuit noise signal amplitude exceeds the effective Doppler signal amplitude, the noise signal is misjudged as an effective signal to thereby calculate an erroneous speed value. Therefore, it is necessary to suppress the circuit noise signal. Although the noise signals are randomly distributed at each frequency point of the power spectrum, the shape of the envelope of the noise signals in the power spectrum does not change. According to the distribution characteristics of the noise signals, the spectrum processing module extracts the envelope of the noise signals. In the static placement process of the velocimeter, no Doppler signal is output, and the power spectrum only contains circuit noise information, so 400 frames of power spectrums are collected as samples, each frame of power spectrum consists of 8192 frequency points, and the average amplitude of each frequency point of the power spectrum is calculated and expressed by a formula (1): Wherein F i represents the power spectrum of the i frame, and the obtained average p