Single-channel signal demodulation method for target displacement measurement of SSB low-intermediate frequency radar

Abstract

The invention provides a single-channel signal demodulation method for target displacement measurement of an SSB low-intermediate frequency radar, and belongs to the technical field of wireless communication. According to the method, odd-even separation, symbol correction and interpolation filtering are carried out on synchronously sampled intermediate frequency signals, and then a track is demodulated by using an arctan algorithm, so that the problems of high sampling rate and I / Q mismatch in the target displacement measurement process of the low-intermediate frequency radar are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communications, and in particular relates to a single-channel signal demodulation method for target displacement measurement of an SSB low-intermediate frequency radar. Background Art

[0002] Since the 20th century, Doppler radar has been widely used in civilian fields such as vital sign monitoring, gesture recognition, mechanical vibration detection, and target positioning. Single-sideband (SSB) low-IF radar is an optimized structure of Doppler radar, which solves the problems of I / Q mismatch and DC bias of conventional Doppler radar. However, traditional low-IF demodulation technology has defects such as high sampling rate, dual-channel mismatch, and complex circuit structure.

[0003] After searching the prior art, it was found that Xujun Ma et al. proposed a hardware-based envelope detection technology in "Envelope Detection for an ADC-Relaxed Double-Sideband Low-IF CW Doppler Radar", which extracts the envelope of the intermediate frequency signal by adding a carrier compensation circuit and an envelope detection circuit to the baseband circuit. However, this technology increases the complexity of the baseband processing circuit during the envelope extraction process, and there is a possibility of I / Q channel phase mismatch. Summary of the invention

[0004] In view of this, the purpose of the present invention is to solve the shortcomings of the prior art and propose a single-channel signal demodulation method for target displacement measurement of SSB low-IF radar, which solves the problems of high sampling rate and I / Q mismatch in low-IF radar target displacement measurement.

[0005] The object of the present invention can be achieved by the following technical scheme: A single-channel signal demodulation method for target displacement measurement of SSB low-intermediate frequency radar comprises the following steps:

[0006] S1. Obtain a single-channel intermediate frequency signal through the SSB low intermediate frequency radar system;

[0007] S2, sampling the single-channel intermediate frequency signal to obtain a single-channel digital signal;

[0008] S3, performing parity check separation and symbol correction on the single-channel digital signal to obtain a zero-interpolation I / Q signal;

[0009] S4, performing interpolation filtering to obtain a zero-frequency I / Q signal;

[0010] S5. Use the arctangent algorithm to demodulate and obtain the target trajectory.

[0011] Preferably, the SSB low intermediate frequency radar system comprises: an active crystal oscillator XO, a phase-locked loop PLL1, a phase-locked loop PLL2, a voltage-controlled oscillator VCO1, a voltage-controlled oscillator VCO2, a radio frequency transmitting module Tx, a radio frequency receiving module Rx, a mixer Mixer, an amplifier circuit AMP, a controller MCU and a host computer PC, wherein the active crystal oscillator XO is respectively connected to the signal input ends of the controller MCU, the phase-locked loop PLL1 and the phase-locked loop PLL2; the signal output end of the phase-locked loop PLL1 is connected to the signal input end of the voltage-controlled oscillator VCO1, and the signal output end of the voltage-controlled oscillator VCO1 is connected to the signal input end of the voltage-controlled oscillator VCO1. The signal output end is connected to the RF transmitting module Tx; the signal output end of the phase-locked loop PLL2 is connected to the signal input end of the voltage-controlled oscillator VCO2, the signal output end of the voltage-controlled oscillator VCO2 is connected to the signal input end of the mixer Mixer, and the signal output end of the RF receiving module Rx is connected to the signal input end of the mixer Mixer; the signal output end of the mixer Mixer is connected to the signal input end of the amplifier circuit AMP, the signal output end of the amplifier circuit AMP is connected to the signal input end of the controller MCU, and the signal output end of the controller MCU is connected to the host computer PC.

[0012] Preferably, the controller MCU is configured with phase-locked loops PLL1, PLL2 and their corresponding voltage-controlled oscillators VCO1, VCO2, to lock two single-frequency signals with a frequency difference of intermediate frequency, and transmit frequency f c +f I , local oscillator frequency f c and the intermediate frequency f I .

[0013] Preferably, the mixer Mixer mixes and converts the signal sent by the RF receiving module Rx and the signal sent by the voltage controlled oscillator VCO2 into a single-channel intermediate frequency signal, and the single-channel intermediate frequency signal is s IF (t) = A IF cos[2πf I t-4πd(t) / λ+θ d ]=cos(2πf I t)I(t)+sin(2πf I t)Q(t), where: A IF is the signal amplitude, λ is the wavelength, f I is the intermediate frequency, θ d is the initial phase, t is the time, d(τ) is the distance from the target to the radar, I(t) = A IF cos[4πd(t) / λ-θ d ], Q(t) = A IF sin[4πd(t) / λ-θ d ].

[0014] Preferably, the sampling rate used in the step S2 is f s =4f I / (2m-1). m refers to any positive integer. As long as the sampling rate is greater than twice the signal bandwidth, m can be a larger positive integer to reduce the sampling rate.

[0015] Preferably, the step S3 is specifically: multiplying the digital signal by using cos[n(2m-1)π / 2] and sin[n(2m-1)π / 2] functions. n is based on the sampling rate f s The index value of the sampled digital signal, n = t × f s , its value is 0, 1, 2…

[0016] Preferably, the step S4 uses a FIR low-pass filter to perform interpolation filtering.

[0017] Preferably, the inverse tangent algorithm demodulation is specifically as follows: Where c is the speed of light, f c is the transmitted signal frequency, f I is the intermediate frequency, x[n] is the target trajectory, and I(n) and Q(n) are zero-frequency I / Q signals.

[0018] Compared with the prior art, the present invention has the following advantages: in the single-channel signal demodulation process of the SSB low intermediate frequency radar, the present invention separates the single-channel signal sequence according to the odd and even indexes, corrects the positive and negative signs of the two groups of sequences, and finally obtains the continuous wave radar signal by interpolation filtering, thereby effectively solving the problems of high sampling rate and I / Q mismatch faced by the low intermediate frequency radar in the process of demodulating the intermediate frequency signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of SSB low-IF radar system for synchronous sampling;

[0020] Figure 2 is a flow chart of a single-channel signal demodulation method based on synchronous sampling;

[0021] Figure 3 Diagram of the setup for the slide table measurement experiment;

[0022] Figure 4 This is the measurement result of the sinusoidal motion of the slide with an amplitude of 4mm and a frequency of 2Hz;

[0023] Figure 5 This is the measurement result of the sinusoidal motion of the slide with an amplitude of 20mm and a frequency of 0.5Hz;

[0024] Figure 6 This is a schematic diagram of the respiratory and heartbeat monitoring experiment;

[0025] Figure 7This is the result of respiratory and heartbeat monitoring. DETAILED DESCRIPTION

[0026] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but are not to be construed as limiting the present invention.

[0027] like Figure 1 As shown, the SSB low-IF radar system sampled in this embodiment includes: an active crystal oscillator XO, a phase-locked loop PLL1, a phase-locked loop PLL2, a voltage-controlled oscillator VCO1, a voltage-controlled oscillator VCO2, a radio frequency transmitting module Tx, a radio frequency receiving module Rx, a mixer Mixer, an amplifier circuit AMP, a controller MCU and a host computer PC, wherein the active crystal oscillator XO is respectively connected to the signal input ends of the controller MCU, the phase-locked loop PLL1 and the phase-locked loop PLL2; the signal output end of the phase-locked loop PLL1 is connected to the signal input end of the voltage-controlled oscillator VCO1, and the voltage-controlled oscillator VCO The signal output end of the phase-locked loop PLL2 is connected to the signal input end of the voltage-controlled oscillator VCO2, the signal output end of the voltage-controlled oscillator VCO2 is connected to the signal input end of the mixer Mixer, and the signal output end of the RF receiving module Rx is connected to the signal input end of the mixer Mixer; the signal output end of the mixer Mixer is connected to the signal input end of the amplifier circuit AMP, the signal output end of the amplifier circuit AMP is connected to the signal input end of the controller MCU, and the signal output end of the controller MCU is connected to the host computer PC. The active crystal oscillator XO provides a reference signal for the ADC and two phase-locked loops in the controller MCU to ensure synchronization of the three. The MCU is configured with two phase-locked loops and corresponding voltage-controlled oscillators to generate two RF signals with an intermediate frequency difference. The RF transmitting module Tx transmits the transmission signal to the detection target and scatters it, generating a reflection signal containing the motion information of the detection target. The RF receiving module Rx receives the signal, amplifies it, and converts it into a single-channel intermediate frequency signal through a mixer with the local oscillator signal sent by the voltage-controlled oscillator VCO2. After amplification by the amplifier circuit AMP and synchronous sampling by the ADC in the MCU, the host computer restores the motion trajectory of the detection target.

[0028] The controller MCU configures the phase-locked loop PLL1, phase-locked loop PLL2 and its corresponding voltage-controlled oscillator VCO1, voltage-controlled oscillator VCO2 to lock two single-frequency signals with a frequency difference of intermediate frequency, and transmit frequency f c +f I , local oscillator frequency f c and the intermediate frequency f I .

[0029] like Figure 2 As shown, this embodiment relates to the single-channel signal demodulation technology of the above system, and the specific steps include:

[0030] S1. Obtain a single-channel intermediate frequency signal through the above-mentioned SSB low intermediate frequency radar system. The single-channel intermediate frequency signal is mixed and frequency-converted by the mixer Mixer in the above-mentioned SSB low intermediate frequency radar system by mixing the signal sent by the RF receiving module Rx and the signal sent by the voltage controlled oscillator VCO2 into a single-channel intermediate frequency signal. The single-channel intermediate frequency signal is s IF (t) = A IF cos[2πf I t-4πd(t) / λ+θ d ]=cos(2πf I t)I(t)+sin(2πf I t)Q(t), where: A IF is the signal amplitude, λ is the wavelength, f I is the intermediate frequency, θ d is the initial phase, t is the time, d(τ) is the distance from the target to the radar, I(t) = A IF cos[4πd(t) / λ-θ d ], Q(t) = A IF sin[4πd(t) / λ-θ d ].

[0031] S2, sampling the single-channel intermediate frequency signal to obtain a single-channel digital signal, which is obtained by sampling the single-channel intermediate frequency signal in step S1 at a sampling rate f s =4f I / (2m-1) is used for sampling.

[0032] S3, performing parity check separation and sign correction on the single-channel digital signal to obtain a zero-interpolated I / Q signal. The specific method is: multiplying the single-channel digital signal with cos[n(2m-1)π / 2] and sin[n(2m-1)π / 2] functions.

[0033] S4. Use a FIR low-pass filter to perform interpolation filtering on the two groups of signals to obtain a continuous wave radar signal, that is, a zero-frequency I / Q signal.

[0034] S5. Demodulate the zero-frequency I / Q signal obtained in step S4 using an inverse tangent algorithm to obtain the target trajectory. The formula is as follows: Where c is the speed of light, x[n] is the target trajectory, and f c +f I is the transmit frequency, I(n) and Q(n) are zero-frequency I / Q signals.

[0035] The accuracy of the above method is demonstrated by testing the motion of a standard slide (Zaber T-NA08A50-KT04U):

[0036] Parameter configuration: lock two single-frequency signals with a frequency difference of intermediate frequency, and transmit frequency f c +f I , local oscillator frequency f c and the intermediate frequency f I .

[0037] like Figure 3 As shown, the radar board is placed 30cm in front of the radar, and the slide table performs standard sinusoidal motions with an amplitude of 4mm and a frequency of 2Hz and an amplitude of 20mm and a frequency of 0.5Hz. The measured experimental results are shown in Figure 4 , Figure 5 As shown. Where (a) is the digital intermediate frequency signal obtained by synchronous sampling, (b) is the orthogonal signal of the continuous wave radar extracted by the present invention, (c) is the comparison between the motion trajectory obtained by demodulation and the actual trajectory, and (d) is the normalized spectrum of the motion trajectory. By comparison, it is found that the high linear phase demodulation technology proposed in the present invention can completely restore the target motion trajectory, and the root mean square errors are only 0.0581mm and 0.2015mm respectively.

[0038] like Figure 6 As shown, the subject sits about 30cm in front of the radar. The radar is aimed at the subject's chest to detect his breathing and heartbeat. Figure 7 The measurement results are shown, where (a) is a single-channel digital signal obtained by synchronous sampling, (b) is an orthogonal signal of a continuous wave radar extracted by the present invention, (c) is a motion trajectory obtained by demodulating the orthogonal signal of the continuous wave radar using an arctan algorithm, and (d) is a normalized spectrum of the motion trajectory. The breathing and heartbeat trajectories of the subject can be seen in Figure (c), and the breathing component, second harmonic, third harmonic and heartbeat component of the subject can be seen in the spectrum.

[0039] Compared with the prior art, the present invention separates the single-channel signal sequence according to the odd and even indexes, corrects the positive and negative signs of the two groups of sequences, and finally obtains the continuous wave radar signal by interpolation filtering during the single-channel signal demodulation process of the SSB low intermediate frequency radar, thereby solving the problems of high sampling rate and I / Q mismatch faced by the low intermediate frequency radar in the process of demodulating the intermediate frequency signal.

[0040] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A single-channel signal demodulation method for target displacement measurement of SSB low-intermediate frequency radar, comprising the following steps: S1. Obtain a single-channel intermediate frequency signal through the SSB low intermediate frequency radar system; S2, sampling the single-channel intermediate frequency signal to obtain a single-channel digital signal; S3, performing parity check separation and symbol correction on the single-channel digital signal to obtain a zero-interpolation I / Q signal; S4, performing interpolation filtering to obtain a zero-frequency I / Q signal; S5. Use the arctangent algorithm to demodulate and obtain the target trajectory.

2. A single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to any one of claim 1, characterized in that: The SSB low intermediate frequency radar system includes: an active crystal oscillator XO, a phase-locked loop PLL1, a phase-locked loop PLL2, a voltage-controlled oscillator VCO1, a voltage-controlled oscillator VCO2, a radio frequency transmitting module Tx, a radio frequency receiving module Rx, a mixer Mixer, an amplifier circuit AMP, a controller MCU and a host computer PC. The active crystal oscillator XO is respectively connected to the signal input ends of the controller MCU, the phase-locked loop PLL1 and the phase-locked loop PLL2; the signal output end of the phase-locked loop PLL1 is connected to the signal input end of the voltage-controlled oscillator VCO1, and the signal output end of the voltage-controlled oscillator VCO1 is connected to the signal input end of the voltage-controlled oscillator VCO2. The output end is connected to the RF transmitting module Tx; the signal output end of the phase-locked loop PLL2 is connected to the signal input end of the voltage-controlled oscillator VCO2, the signal output end of the voltage-controlled oscillator VCO2 is connected to the signal input end of the mixer Mixer, and the signal output end of the RF receiving module Rx is connected to the signal input end of the mixer Mixer; the signal output end of the mixer Mixer is connected to the signal input end of the amplifier circuit AMP, the signal output end of the amplifier circuit AMP is connected to the signal input end of the controller MCU, and the signal output end of the controller MCU is connected to the host computer PC.

3. The single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to claim 2 is characterized in that: The controller MCU is configured with phase-locked loops PLL1, PLL2 and their corresponding voltage-controlled oscillators VCO1, VCO2, to lock two single-frequency signals with a frequency difference of intermediate frequency, and transmit frequency f c +f I , local oscillator frequency f c and the intermediate frequency f I .

4. A single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to claim 3, characterized in that: The mixer Mixer mixes the signal sent by the RF receiving module Rx and the signal sent by the voltage controlled oscillator VCO2 into a single-channel intermediate frequency signal. The single-channel intermediate frequency signal is s IF (t) = A IF cos[2πf I t-4πd(t) / λ+θ d ]=cos(2πf I t)I(t)+sin(2πf I t)Q(t), where: A IF is the signal amplitude, λ is the wavelength, f I is the intermediate frequency, θ d is the initial phase, t is the time, d(τ) is the distance from the target to the radar, I(t) = A IF cos[4πd(t) / λ-θ d ], Q(t) = A IF sin[4πd(t) / λ-θ d ].

5. A single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to claim 3 or 4, characterized in that: The sampling rate used in the S2 step is f s =4f I / (2m-1), where m is any positive integer that satisfies the sampling rate to be greater than twice the signal bandwidth.

6. A single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to claim 5, characterized in that: The step S3 is specifically as follows: multiplying the single-channel digital signal by cos[n(2m-1)π / 2] and sin[n(2m-1)π / 2] functions, where n is the sampling rate f. s The index value of the sampled digital signal, n = t × f s (The values ​​are 0, 1, 2…).

7. A single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to claim 1 or 2 or 3 or 4, characterized in that: The step S4 uses a FIR low-pass filter to perform interpolation filtering.

8. The single-channel signal demodulation method for target displacement measurement of SSB low intermediate frequency radar according to claim 6, characterized in that: The inverse tangent algorithm demodulation is specifically as follows: Where c is the speed of light, x[n] is the target trajectory, and I(n) and Q(n) are zero-frequency I / Q signals.

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