Phase-coded unsaturated modulation method, device, laser radar ranging and speed measurement method, and laser radar system

Abstract

The present invention relates to a phase-coded desaturated modulation method, device, laser radar ranging and velocity measurement method, and laser radar system. Phase desaturated modulation is used to ensure that a modulated laser signal simultaneously contains a single-frequency component and a phase-modulated component with the same or similar energy ratio. The single-frequency component can be used to obtain the relative motion velocity between the platform and the target and to compensate for the frequency drift of the seed laser. The obtained relative Doppler frequency is used to construct a matched filter function, which performs pulse compression on the phase-coded signal to obtain the distance information between the target and the platform. This invention can simultaneously perform ranging and velocity measurement with high accuracy, low error, minimal computational effort, and low system complexity.

Description

Technical Field

[0001] The present invention relates to the field of laser radar, and in particular to a phase-coded unsaturated modulation method and device, a laser radar ranging and speed measurement method, and a laser radar system. Background Art

[0002] Pulse compression is an important system in modern radar. It effectively solves the contradiction between radar range resolution and average power, and is widely used in modern radar. There are three typical pulse compression signals: linear frequency modulation (LFM), nonlinear frequency modulation (NLFM), and phase-coded keying (PSK). Phase-coded signals, with a small time-bandwidth product, offer a large primary-to-secondary ratio and excellent compression performance, making them widely used. Furthermore, because they use a pseudo-random sequence, they facilitate signal agility, which improves the radar system's anti-interception capability. However, a drawback is that during the pulse compression of target echo signals, phase-coded signals are subject to Doppler modulation due to variations in the carrier frequency of the target and platform, as well as in the seed laser's round-trip time. The Doppler effect of the relative motion between the platform and target causes the matched filter function to become completely mismatched, making it impossible to obtain relative distance information between the target and platform through the pulse compression process. Phase-coded signals are Doppler-sensitive, and Doppler shift in the echo signal severely impacts pulse compression performance. Therefore, especially in applications such as lidar where the carrier frequency is high, the Doppler shift of the target's relative motion is large, and the seed laser frequency is unstable, compensation for the Doppler effect caused by relative motion between the target and platform is essential. Therefore, it is necessary to improve the existing technology to effectively solve the Doppler sensitivity problem of traditional phase-coded signals while achieving the measurement of the relative motion speed of the target. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a phase-coded unsaturated modulation method, device, laser radar ranging and speed measurement method and laser radar system. Phase unsaturated modulation is adopted to make the modulated laser signal have a single-frequency component and a phase-coded modulation component at the same time. The single-frequency component can be used to obtain the relative motion speed between the platform and the target and to compensate for the frequency drift of the seed laser. The obtained relative Doppler frequency is used to construct a matched filter function, and the phase-coded modulation signal is pulse compressed to obtain the distance information between the target and the platform.

[0004] The technical solution of the present invention is: a phase-encoded unsaturated modulation method, which performs phase-encoded modulation on a single-frequency laser, wherein the phase-encoded modulation form is two-phase or multi-phase, and the modulation depth is phase-unsaturated modulation.

[0005] Furthermore, when the phase coding modulation form is a binary code, the signal modulation form is:

[0006]

[0007]

[0008] Among them, Sig(t) is the output laser modulation signal, A is the laser signal amplitude, f0 is the laser carrier frequency, is a phase modulation signal, n is an integer, and η is 0.2 to 0.8.

[0009] Furthermore, η is 0.4 to 0.6.

[0010] Furthermore, the laser signal after phase-encoded unsaturated modulation includes a single-frequency spectrum component and a phase-encoded modulated broadband spectrum component. The broadband spectrum component of phase-encoded modulation is the phase-encoded spectrum component, and the energy proportions of the two are the same or close.

[0011] Furthermore, the energy proportion of the single-frequency spectrum component is 40%-60%.

[0012] The present invention also provides a phase-coded unsaturated modulation device for implementing the above-mentioned phase-coded unsaturated modulation method, which is characterized by comprising a laser generator, a laser phase modulator and a signal generator, the laser generator being used to emit a single-frequency laser of constant intensity, the laser emission end of the laser generator being connected to the optical input end of the laser phase modulator, the signal generator being used to generate a phase-coded modulated electrical signal, the electrical signal output end of the signal generator being connected to the signal input end of the laser phase modulator, and the single-frequency laser being phase-coded unsaturated modulated in the laser phase modulator.

[0013] The present invention also provides a laser radar ranging and speed measurement method, based on the above-mentioned phase coding unsaturated modulation method, comprising the following steps:

[0014] Step S1: performing phase-encoded unsaturated modulation on a single-frequency laser;

[0015] Step S2: The laser signal after phase-encoded unsaturated modulation and amplification is emitted, and the echo laser reflected by the target is heterodyned with the single-frequency laser and subjected to photoelectric conversion to obtain a heterodyned intermediate frequency electrical signal;

[0016] Step S3: Processing the intermediate frequency electrical signal and converting it into an intermediate frequency complex signal;

[0017] Step S4: Perform Fourier transform on the intermediate frequency complex signal to obtain a signal spectrum;

[0018] Step S5: Perform data processing on the signal spectrum and intermediate frequency complex signal obtained after Fourier transform to obtain speed information and distance information, thereby completing the laser radar ranging and speed measurement.

[0019] Furthermore, the step S1 also includes pulse width modulation of the single-frequency laser. The laser signal is in the form of continuous wave, quasi-continuous wave or pulse wave after pulse width modulation. The laser frequency can also be shifted during the modulation process.

[0020] Furthermore, in step S3, the complex signal conversion process is implemented using a hardware structure or a data processing algorithm.

[0021] Furthermore, the step S4 further includes the following steps:

[0022] S41: Compare the single-frequency spectrum component obtained after Fourier transform of the intermediate frequency complex signal with the frequency signal strength threshold to obtain an array of single-frequency peak points with an intensity greater than the frequency signal strength threshold, thereby obtaining the Doppler magnitude and direction of the relative motion between the laser radar and the target;

[0023] S42: A velocity array can be obtained by processing the single-frequency peak point array, and the velocity array reflects the velocity information;

[0024] S43: Using a single-frequency peak point array to construct a matched filter function, the matched filter function and the phase-coded spectrum component in the intermediate frequency complex signal are pulse compressed, and the compressed data information is compared with the distance signal strength threshold. Points with a strength greater than the distance signal strength threshold form a distance array, which reflects the distance information;

[0025] S44: Output speed array and distance array.

[0026] The present invention also provides a laser radar system for executing the above-mentioned laser radar ranging and speed measurement method, comprising: a laser generator, a laser phase modulator, a laser amplifier, a laser demodulator, a photodetector, a data acquisition and processor, and a signal generator. The laser generator is used to emit single-frequency laser. The laser emission end of the laser generator is connected to the optical input end of the laser demodulator and the optical input end of the laser phase modulator. The signal generator is used to generate a phase-coded modulated electrical signal. The electrical signal output end of the signal generator is connected to the signal input end of the laser phase modulator. The optical output end of the laser phase modulator is connected to the optical input end of the laser amplifier. The optical output end of the laser amplifier is connected to a light receiving and transmitting circuit. The light receiving and transmitting circuit transmits the laser output by the laser amplifier and simultaneously introduces the received target reflective echo signal into the optical input end of the laser demodulator. The optical output end of the laser demodulator is connected to the photodetector. The photodetector is connected to a data acquisition and processor.

[0027] Furthermore, a pulse width modulator may be provided, and the pulse width modulator is provided between the laser generator and the laser phase modulator. The pulse width modulator may also have a function of shifting the frequency of the laser signal.

[0028] Furthermore, a circulator may be provided, and the circulator is provided between the laser amplifier and the light transmitting and receiving path.

[0029] The present invention has the following beneficial effects:

[0030] 1) Phase-coded unsaturated modulation signals can simultaneously obtain the relative velocity and distance information between the target and the platform. Compared with existing phase-coded techniques, this can achieve velocity / Doppler dimension detection, further improving the Doppler tolerance of existing phase-coded modulation techniques.

[0031] 2) The technical solution of the present invention can obtain target motion velocity information even when the echo signal has an extremely low signal-to-noise ratio (<0dB). Compared with the existing solution of detecting motion velocity by multiplying the intermediate frequency orthogonal phase coded signal, the system has higher detection sensitivity.

[0032] 3) In the speed and ranging dimensions, the unsaturated modulated signal has the same carrier, generation time, and propagation path. Therefore, the errors caused by Doppler and environmental errors on the ranging and speed signal components are exactly the same. These errors are common-mode errors and can be eliminated through subsequent signal processing.

[0033] 4) Phase-coded unsaturated modulation only requires one Fourier transform of the echo signal to obtain the target relative motion Doppler frequency, eliminating the need for complex iterative signal processing and effectively reducing the amount of system computation.

[0034] 5) The technical solution of the present invention adopts an unsaturated modulation method, and only one-stage modulator is used to complete unsaturated phase-coded unsaturated modulation, which greatly reduces the system complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the time domain signal form after phase-coded unsaturated modulation heterodyne.

[0036] Figure 2 It is the frequency domain signal form after phase-coded unsaturated modulation heterodyne.

[0037] Figure 3 It is a system diagram of a phase-coded unsaturated modulation device.

[0038] Figure 4 This is a flow chart of the laser radar ranging and speed measurement method based on phase-coded unsaturated modulation.

[0039] Figure 5 It is a schematic diagram of the laser radar ranging and speed measurement system.

[0040] Among them, the above-mentioned drawings include the following figure marks: 1. Single-frequency spectrum component; 2. Phase-coded spectrum component; 3. Single-frequency laser; 4. Echo laser; 5. Intermediate-frequency electrical signal; 6. Intermediate-frequency complex signal; 7. Signal spectrum; 8. Frequency signal strength threshold; 9. Single-frequency peak point array; 10. Matched filter function; 11. Pulse compression; 12. Distance signal strength threshold; 13. Velocity array; 14. Distance array; 15. Loop operation; 16. Laser generator; 17. Modulator; 18. Laser phase modulator; 19. Laser amplifier; 20. Circulator; 21. Transmitting and transmitting light path; 22. Laser demodulator; 23. Photodetector; 24. Data acquisition and processor; 25. Signal generator. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] Example 1

[0043] See also Figure 1-2 A phase-coded desaturation modulation method includes: performing phase-coded modulation on a single-frequency laser output by a laser generator 16, wherein the phase-coded modulation form is two-phase or multi-phase, and the modulation depth is phase desaturation modulation. When the phase coding form is a two-phase code, the signal modulation form of the phase desaturation modulation is:

[0044]

[0045]

[0046] Among them, Sig(t) is the output laser modulation signal, A is the laser signal amplitude, f0 is the laser carrier frequency, is a phase modulation signal, n is an integer (such as -1, 0, 1...), and η is 0.2~0.8 (preferably 0.4~0.6).

[0047] The laser signal after phase-coded unsaturated modulation includes a single-frequency spectrum component 1 and a phase-coded modulated broadband spectrum component. The phase-coded modulated broadband spectrum component is the phase-coded spectrum component 2. The energy proportions of the two are the same or close. The energy proportion of the single-frequency spectrum component 1 is 40%-60%.

[0048] Example 2

[0049] See also Figure 3A phase-coded unsaturated modulation device includes a laser generator 16, a laser phase modulator 18 and a signal generator 25. The laser generator 16 is used to emit a single-frequency laser of constant intensity. The laser emitting end of the laser generator 16 is connected to the optical input end of the laser phase modulator 18. The signal generator 25 is used to generate a phase-coded modulated electrical signal. The electrical signal output end of the signal generator 25 is connected to the signal input end of the laser phase modulator 18. The single-frequency laser is phase-coded unsaturated modulated in the laser phase modulator 18. The laser signal after phase-coded unsaturated modulation includes a single-frequency spectrum component and a phase-coded modulated broadband spectrum component, and the energy proportions of the two are the same or close.

[0050] Example 3

[0051] See attached Figure 4 A laser radar ranging and speed measurement method specifically includes the following steps:

[0052] Step S1: using the method in Example 1 to perform phase-encoded unsaturated modulation on the single-frequency laser output by the laser generator 16;

[0053] Step S1 also includes modulating the pulse width and frequency of the single-frequency laser output by the laser generator 16 .

[0054] Step S2: The laser signal after phase-encoded unsaturated modulation and amplification is emitted, and the echo laser 4 reflected by the target is heterodyned and mixed with the single-frequency laser 3, and photoelectric conversion is performed to obtain a heterodyned intermediate frequency electrical signal 5; the intermediate frequency electrical signal is processed and converted into an intermediate frequency complex signal 6;

[0055] The laser demodulation process can be implemented using a hardware structure such as an orthogonal demodulator, or it can be implemented using a 3dB coupler combined with data processing algorithms such as Hilbert transform;

[0056] Step S3: Perform Fourier transform on the intermediate frequency complex signal 6 to obtain a signal spectrum 7;

[0057] Step S4: Perform data processing on the signal spectrum 7 and the intermediate frequency complex signal 6 obtained after Fourier transform to obtain speed information and distance information, thereby completing the laser radar ranging and speed measurement.

[0058] The data processing in step S4 specifically includes the following steps:

[0059] Step S41: Compare the single-frequency spectrum components in the signal spectrum 7 obtained after Fourier transform of the laser signal with the frequency signal strength threshold 8 to obtain an array 9 of single-frequency peak points whose intensity is greater than the frequency signal strength threshold 8, thereby obtaining the Doppler magnitude and direction of the relative motion between the laser radar and the target;

[0060] Step S42: The speed array 13 can be obtained by processing the single-frequency peak point array 9. The speed array 13 reflects the speed information.

[0061] Step S43: Constructing a matched filter function 10 using each element in the single-frequency peak point array 9. Performing pulse compression 11 on the phase-coded spectrum component of the intermediate frequency complex signal 6 with the matched filter function 10. Comparing the compressed data information with a distance signal strength threshold 12. Points with a strength greater than the distance signal strength threshold 12 form a distance array 14, which represents the distance information.

[0062] Step S44: Output the speed array 13 and the distance array 14.

[0063] Example 4

[0064] See attached Figure 5 A laser radar system for executing the laser radar ranging and speed measurement method described in Example 3, specifically comprising the following components: a laser generator 16, a laser phase modulator 18, a laser amplifier 19, a light-receiving and light-emitting circuit 21, a laser demodulator 22, a photodetector 23, a data acquisition and processor 24, and a signal generator 25;

[0065] The laser generator 16 is used to emit a single-frequency laser. The laser emitting end of the laser generator 16 is connected to the optical input end of the laser phase modulator 18 and the optical input end of the laser demodulator 22. The signal generator 25 is used to emit a phase-coded modulated electrical signal. The signal output of the signal generator 25 is connected to the signal input end of the laser phase modulator 18. The single-frequency laser is phase-coded unsaturated modulated in the laser phase modulator 18. The laser signal after phase-coded unsaturated modulation includes a single-frequency spectrum component and a phase-coded modulated broadband spectrum component, and the energy ratio occupied by the two is the same or close.

[0066] The optical output end of the laser phase modulator 18 is connected to the optical input end of the laser amplifier 19, and the optical output end of the laser amplifier 19 is connected to the light receiving and light circuit 21. The light receiving and light circuit 21 transmits the laser signal generated by the laser amplifier 19, and at the same time introduces the received target reflection echo signal 4 into the optical input end of the laser demodulator 22. The optical output end of the laser demodulator 22 is connected to the photodetector 23, and the photodetector 23 is connected to the data acquisition and processor 24. The light receiving and light circuit 21 is a device for laser emission and echo laser reception.

[0067] The above-mentioned laser radar system may further be provided with a modulator 17 , which is provided between the laser generator 16 and the laser phase modulator 18 , or between the laser generator 16 and the laser demodulator 22 .

[0068] The modulator 17 is a pulse width modulator, and the laser signal is in the form of a continuous wave, a quasi-continuous wave or a pulse wave after pulse width modulation; or the modulator 17 is a pulse frequency modulator, which can frequency modulate the input laser signal; or the modulator 17 is a pulse width frequency modulator, which can simultaneously modulate the pulse width and frequency of the input laser signal.

[0069] The above-mentioned laser radar system may further be provided with a circulator 20 , which is provided between the laser amplifier 19 and the light transmitting and receiving path 21 .

[0070] The laser demodulator 22 can use orthogonal demodulation to obtain four optical mixing signals with a phase difference of 90°, or use 3dB coupling to obtain two optical mixing signals with a phase difference of 180°.

[0071] If the laser demodulator 22 is a quadrature demodulator, two photodetectors 23 need to be connected, with signals with a phase difference of 0° and 180° entering one detector and signals with a phase difference of 90° and 270° entering the other detector.

[0072] If the laser demodulator 22 is a 3dB coupler, it needs to be connected to a photodetector 23 .

[0073] The laser generator 16 outputs a single-frequency laser, which is modulated by the pulse width / frequency modulator 17 and then enters the laser phase modulator 18 for phase-coded unsaturated modulation. The laser signal after phase-coded unsaturated modulation enters the circulator 20 through the laser amplifier 19. The circulator 20 is connected to the light-receiving and light-emitting circuit 21 for laser emission. The target echo received by the light-receiving and light-emitting circuit 21 is connected to the circulator 20 to form the echo laser 4. The single-frequency laser 3 and the echo laser 4 enter the laser demodulator 22 for heterodyne demodulation. The demodulated laser signal enters the photodetector 23 and the data acquisition and processor 24 for signal processing.

[0074] In the heterodyne demodulation process, the laser demodulator 22 may be an orthogonal demodulator to obtain four optical signals with a phase difference of 90°, or a 3dB coupler to obtain two optical signals with a phase difference of 180°.

[0075] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A laser radar ranging and speed measurement method, characterized in that: The following steps are involved: Step S1: performing phase-coded unsaturated modulation on a single-frequency laser based on a phase-coded unsaturated modulation method; in the phase-coded unsaturated modulation method, the phase-coded modulation form is two-phase or multi-phase, and the modulation depth is phase unsaturated modulation; when the phase-coded modulation form is a two-phase code, the signal modulation form is: Among them, Sig(t) is the output laser modulation signal, A is the laser signal amplitude, f0 is the laser carrier frequency, is a phase modulation signal, n is an integer, and η is 0.2 to 0.8; Step S2: emitting a laser signal after phase-coded unsaturated modulation and amplification, performing heterodyne mixing and photoelectric conversion on the echo laser reflected by the target and the single-frequency laser to obtain a heterodyne intermediate frequency electrical signal; processing the intermediate frequency electrical signal and converting it into an intermediate frequency complex signal; Step S3: Perform Fourier transform on the intermediate frequency complex signal to obtain a signal spectrum; Step S4: Processing the signal spectrum and intermediate frequency complex signal obtained after Fourier transform to obtain speed information and distance information, thereby completing the laser radar ranging and speed measurement; The step S4 further includes the following steps: S41: Compare the single-frequency spectrum component in the signal spectrum with the frequency signal strength threshold to obtain an array of single-frequency peak points whose intensity is greater than the frequency signal strength threshold, thereby obtaining the Doppler magnitude and direction of the relative motion between the laser radar and the target; S42: obtaining a velocity array by processing the single-frequency peak point array, where the velocity array reflects velocity information; S43: Using a single-frequency peak point array to construct a matched filter function, the matched filter function and the phase-coded spectrum component in the intermediate frequency complex signal are pulse compressed, and the compressed data information is compared with the distance signal strength threshold. Points with a strength greater than the distance signal strength threshold form a distance array, and the distance array reflects the distance information; S44: Output speed array and distance array.

2. The laser radar ranging and speed measurement method according to claim 1, characterized in that: The step S1 further includes performing pulse width modulation on the single-frequency laser, and the laser signal is in the form of a continuous wave, a quasi-continuous wave or a pulse wave after the pulse width modulation.

3. The laser radar ranging and speed measurement method according to claim 1, wherein: The step S1 further includes frequency modulation of the single-frequency laser, and the laser signal after frequency modulation has a frequency difference with the original single-frequency laser.

4. The laser radar ranging and speed measurement method according to claim 1, wherein: In step S2, the process of obtaining the intermediate frequency complex signal is implemented by using a hardware optical path structure or a data processing algorithm.

5. The laser radar distance and speed measurement method according to claim 1, wherein: η is 0.4~0.

6.

6. The laser radar distance and speed measurement method according to claim 1, characterized in that: The laser signal after phase-encoded unsaturated modulation includes a single-frequency spectrum component and a phase-encoded modulated broadband spectrum component. The broadband spectrum component of phase-encoded modulation is also the phase-encoded spectrum component, and the energy proportions of the two are the same or close.

7. The laser radar distance and speed measurement method according to claim 4, characterized in that: The energy proportion of the single-frequency spectrum component is 40%-60%.

8. A phase-coded unsaturated modulation device, used to implement the laser radar ranging and speed measurement method according to any one of claims 1 to 7, characterized in that: The invention comprises a laser generator, a laser phase modulator and a signal generator. The laser generator is used to emit a single-frequency laser. The laser emission end of the laser generator is connected to the optical input end of the laser phase modulator. The signal generator is used to generate a phase-coded modulated electrical signal. The electrical signal output end of the signal generator is connected to the signal input end of the laser phase modulator. The single-frequency laser is subjected to phase-coded unsaturated modulation in the laser phase modulator.

9. A laser radar system for executing the laser radar ranging and speed measurement method according to any one of claims 1 to 7, characterized in that: include: A laser generator (16), a laser phase modulator (18), a laser amplifier (19), a laser demodulator (22), a photodetector (23), a data acquisition and processor (24) and a signal generator (25), wherein the laser generator (16) is used to emit a single-frequency laser, the laser emission end of the laser generator (16) is connected to the optical input end of the laser demodulator (22) and the optical input end of the laser phase modulator (18), the signal generator (25) is used to generate a phase-encoded modulated electrical signal, the electrical signal output end of the signal generator (25) is connected to the signal input end of the laser phase modulator (18), and the The single-frequency laser is subjected to phase-encoded unsaturated modulation in the laser phase modulator (18). The optical output end of the laser phase modulator (18) is connected to the optical input end of the laser amplifier (19). The optical output end of the laser amplifier (19) is connected to a light-receiving and light-emitting circuit (21). The light-receiving and light-emitting circuit (21) transmits the laser signal generated by the laser amplifier (19) and simultaneously introduces the received target reflected echo laser (4) into the optical input end of the laser demodulator (22). The optical output end of the laser demodulator (22) is connected to a photodetector (23). The photodetector (23) is connected to a data acquisition and processor (24).

10. The laser radar system according to claim 9, characterized in that: The laser demodulator (22) is an orthogonal demodulator and is connected to two photodetectors (23) at the same time.

11. The laser radar system according to claim 9, characterized in that: The laser demodulator (22) is a 3dB coupler connected to a photodetector (23).

12. The laser radar system according to claim 9, wherein: A modulator (17) is also provided, and the modulator (17) is provided between the laser generator (16) and the laser phase modulator (18), or between the laser generator (16) and the laser demodulator (22).

13. A laser radar system according to claim 12, characterized in that: The modulator (17) is one of a pulse width modulator, a pulse frequency modulator, and a pulse width frequency modulator.

14. The laser radar system according to claim 9, wherein: A circulator (20) is also provided, and the circulator (20) is provided between the laser amplifier (19) and the light transmitting and receiving path (21).

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