Target distance and speed measurement system and method based on direct detection laser radar compatible with software radio

Abstract

The invention discloses a target distance and speed measurement system and method based on a direct detection laser radar compatible with software radio, and belongs to the technical field of target distance and speed measurement. According to the invention, the problems of low utilization rate of echo light power, complex structure, crosstalk of microwave and optical frequency signals, and low precision of distance measurement and speed measurement in the prior art are solved. According to the improved direct detection laser radar structure compatible with the software radio provided by the invention, a radio frequency signal can be demodulated from echo signal light of the laser radar only by a single square-rate photoelectric detector, so that the structure is simpler; and the frequencies for transmitting and receiving the microwave radio-frequency signals are different, so that the microwave crosstalk of the transmitting end and the receiving end is avoided. Due to the fact that the receiving and transmitting separated optical antenna is adopted, crosstalk of optical frequency signals can be eliminated. Moreover, the method effectively improves the measurement precision of the target distance and speed. The method can be applied to target distance and speed measurement.

Description

Technical Field

[0001] This invention belongs to the field of target distance and velocity measurement technology, specifically relating to a target distance and velocity measurement system and method based on a direct detection lidar with compatible software radio. Background Technology

[0002] In recent years, to address bottlenecks in microwave devices and other areas, microwave photonics has been proposed. It uses optical devices and methods to generate, transmit, process, and measure high-frequency microwave signals, thus leveraging the advantages of optical technology to advance microwave technology. However, as a discipline combining microwave and optical technologies, microwave photonics can also leverage the advantages of microwave technology to advance optical technology. Furthermore, because microwave technology is relatively more advanced and more closely integrated with computer technology, wavelength, bandwidth, modulation, demodulation, encoding, and decoding can all be defined through software programming, leading to advanced technologies such as software-defined radio and software-defined radar. Introducing these advanced microwave technologies into optical technology through microwave photonics methods will undoubtedly play a crucial role in the further development of optical technology.

[0003] In the field of coherent detection lidar, people have begun to use microwave photonics methods to improve its performance in various aspects (S. Gao and R. Hui, “Frequency-modulated continuous-wave lidar using I / Qmodulator for simplified heterodyne detection,” Opt. Lett. 37(11), 2022-2024(2012). and S. Gao, M. Sullivan and R, Hui, “Complex-optical-field lidar system for range and vector velocity measurement,” Opt. Express 20(23), 25867-25875(2012).). Optoelectronic modulators are used to replace the acousto-optic frequency shifters in conventional heterodyne lidar to suppress carrier complex optical field modulation of the emitted laser, thereby using higher bandwidth to linearly modulate one sideband to achieve higher ranging accuracy, while constant radio frequency modulation is performed on the other sideband of the optical signal to achieve target velocity measurement (S. Gao and R. Hui, “Frequency-modulated continuous-wave lidar using I / Q modulator for simplified heterodyne detection,” Opt. Lett. 37(11), 2022-2024(2012). and S. Gao, M. Sullivan and R, Hui, “Complex-optical-field lidar system for range and vector velocity measurement,” Opt. Express 20(23), 25867-25875(2012).).Mach-Zehnder modulators operating in suppressed-carrier double-sideband modulation mode achieve simultaneous ranging and velocity measurement by frequency-dividing and real-time reverse linear frequency modulation of the emitted laser (D. Mo, R. Wang, G. Li, N. Wang, K. Zhang and Y. Wu, “Double-sideband frequency scanning interferometry for long-distance dynamic absolute measurement,” Appl. Phys. B 123(11), 272(2017). and K. Zhang, T. Lv, D. Mo, N. Wang, R. Wang and Y. Wu, “Double sideband frequency scanning interferometry for distance measurement in the outdoor environment,” Opt. Commun. 425, 176-179(2018).). The local oscillator light and the target back-reflected light are combined by a fiber optic 90-degree synthesizer to generate a beat frequency signal. This not only distinguishes the upper and lower sidebands of the signal light in the form of complex signals, thus achieving simultaneous high-precision measurement of distance and velocity, but also completes the conversion of radio frequency signals to baseband signals, reducing the sampling bandwidth of analog-to-digital conversion and further reducing costs. By using unmodulated light to beat frequency with the target back-reflected light on both sides and using the modulated radio frequency signal to perform dechirped mixing with the detector output beat frequency signal, only one AD converter is needed for baseband digital signal acquisition, which can also achieve simultaneous measurement of target distance and velocity (Z. Xu, L. Tang, H. Zhang and S. Pan, “Simultaneous real-time ranging and velocimetry via a dual-sideband chirped lidar,” IEEE Photonics Technol. Lett. 29(24), 2254-2257(2017).).

[0004] Direct-detection lidar, as another important type of lidar, has significant applications in fields such as robot navigation and assisted driving due to its simple and reliable structure (H. Xia, X. Dou, D. Sun, Z. Shu, X. Xue, Y. Han, D. Hu, Y. Han and T. Cheng, “Mid-altitude wind measurements with mobile Rayleigh Doppler lidar incorporating system level optical frequency control method,” Opt. Express 20(14), 15286-15300(2012).). However, few researchers have yet leveraged microwave photonics methods to incorporate the advantages of microwave technology into direct-detection lidar to improve its performance. Patent application CN116973929A discloses a novel direct-detection lidar structure compatible with software-defined radio (SDR). It uses a fiber optic phase modulator, commonly used in microwave photonics, to load a microwave (RF) signal onto the lidar's emitted laser. A combination of a fiber optic Fabry-Perot interferometer and a photodetector demodulates the microwave (RF) signal from the echo signal. The generation of the transmitted microwave (RF) signal, as well as the acquisition and processing of the received microwave (RF) signal, are all handled by a software-defined radio. Since this structure is equivalent to installing a microwave (RF) signal radar on a direct-detection lidar, it retains the advantages of lidar in terms of spatial resolution, while also utilizing the ranging and velocity measurement algorithms of microwave (RF) radar. This gives it some advantages of microwave (RF) technology, such as suitability for high-speed target measurement and software-defined characteristics. However, this direct-detection lidar still has certain shortcomings, such as low echo power utilization, complex structure, crosstalk between microwave (RF) and optical signals, and the need for further improvement in ranging and velocity measurement accuracy. Summary of the Invention

[0005] The purpose of this invention is to address the problems of low echo power utilization, complex structure, crosstalk between microwave and optical frequency signals, and low ranging and velocity measurement accuracy in existing methods. Therefore, this invention proposes a target distance and velocity measurement system and method based on a direct detection lidar compatible with software radio.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] According to one aspect of the present invention, a target range and velocity measurement system based on a direct detection lidar compatible with software radio is provided, the system comprising two parts: an optical path and a circuit.

[0008] The optical path includes a continuous-wave fiber laser, a Mach-Zehnder modulator, a fiber amplifier, a transmitting optical antenna, a receiving optical antenna, and a photodetector; wherein:

[0009] The continuous wave fiber laser is used to generate single-frequency signal light, and the output end of the continuous wave fiber laser is connected to the first input end of the Mach-Zehnder modulator.

[0010] The output of the Mach-Zehnder modulator is connected to the input of the fiber optic amplifier.

[0011] The output end of the fiber amplifier is connected to the input end of the transmitting optical antenna, and the signal emitted from the output end of the transmitting optical antenna illuminates the detection target.

[0012] The signal reflected back from the target enters the input of the receiving optical antenna, and the output of the receiving optical antenna is connected to the input of the photodetector.

[0013] The circuitry includes a computer and software-defined radio;

[0014] The software-defined radio includes an interface controller, a transmit controller, a first digital up-converter, a second digital up-converter, a first digital-to-analog converter, a second digital-to-analog converter, a first low-pass filter, a second low-pass filter, a first local oscillator, a first mixer, a second mixer, a first power amplifier, a second power amplifier, a second local oscillator, a third mixer, a fourth mixer, a third low-pass filter, a fourth low-pass filter, a first analog-to-digital converter, a second analog-to-digital converter, a first digital down-converter, a second digital down-converter, and a receive controller; wherein:

[0015] The computer's output terminal is connected to the interface controller's input / output terminal;

[0016] The output of the interface controller is connected to the input of the transmitter controller;

[0017] The first output terminal of the transmitter controller is connected to the input terminal of the first digital up-converter; the second output terminal of the transmitter controller is connected to the input terminal of the second digital up-converter.

[0018] The output of the first digital-to-digital converter is connected to the input of the first digital-to-analog converter; the output of the second digital-to-digital converter is connected to the input of the second digital-to-analog converter.

[0019] The output of the first digital-to-analog converter is connected to the input of the first low-pass filter; the output of the second digital-to-analog converter is connected to the input of the second low-pass filter.

[0020] The first output terminal of the first local oscillator is connected to the first input terminal of the first mixer; the second output terminal of the first local oscillator is connected to the first input terminal of the second mixer.

[0021] The output terminal of the first low-pass filter is connected to the second input terminal of the first mixer; the output terminal of the second low-pass filter is connected to the second input terminal of the second mixer.

[0022] The output terminals of the first mixer and the second mixer are connected to the input terminal of the first power amplifier;

[0023] The output of the first power amplifier is connected to the second input of the Mach-Zehnder modulator.

[0024] The output terminal of the photodetector is connected to the input terminal of the second power amplifier;

[0025] The output terminal of the second power amplifier is connected to the first input terminal of the third mixer and the first input terminal of the fourth mixer, respectively.

[0026] The first output terminal of the second local oscillator is connected to the second input terminal of the third mixer; the second output terminal of the second local oscillator is connected to the second input terminal of the fourth mixer.

[0027] The output of the third mixer is connected to the input of the third low-pass filter; the output of the fourth mixer is connected to the input of the fourth low-pass filter.

[0028] The output of the third low-pass filter is connected to the input of the first analog-to-digital converter; the output of the first analog-to-digital converter is connected to the input of the first digital down-converter.

[0029] The output of the fourth low-pass filter is connected to the input of the second analog-to-digital converter; the output of the second analog-to-digital converter is connected to the input of the second digital down-converter.

[0030] The output of the first digital down-converter is connected to the first input of the receiver controller; the output of the second digital down-converter is connected to the second input of the receiver controller.

[0031] The output of the receiver controller is connected to the input of the interface controller, and the interface controller is connected to the input of the computer through its input and output terminals.

[0032] According to another aspect of the present invention, a method for measuring target range and velocity based on a direct detection lidar compatible with software radio specifically includes the following steps:

[0033] Two orthogonal digital intermediate frequency (IF) signals are generated by a computer. The two orthogonal IF signals are then passed through a software radio interface controller and a transmitter controller. One signal output from the transmitter controller is then passed through a first digital up-converter, a first digital-to-analog converter, and a first low-pass filter in sequence. The other signal output from the transmitter controller is then passed through a second digital up-converter, a second digital-to-analog converter, and a second low-pass filter in sequence.

[0034] Two orthogonal analog intermediate frequency signals are output using a first low-pass filter and a second low-pass filter;

[0035] Two orthogonal local oscillation radio frequency signals are generated using a first local oscillator. The analog intermediate frequency signal output from the first low-pass filter is mixed with one local oscillation radio frequency signal generated by the first local oscillator using a first mixer. The analog intermediate frequency signal output from the second low-pass filter is mixed with another local oscillation radio frequency signal generated by the first local oscillator using a second mixer to obtain two mixed radio frequency signals.

[0036] The two mixed radio frequency signals are then combined into one radio frequency signal, which is then amplified by the first power amplifier and input into the Mach-Zehnder modulator.

[0037] The optical signal generated by the continuous wave fiber laser is transmitted to the Mach-Zehnder modulator. After the optical signal is amplitude modulated in the Mach-Zehnder modulator, the optical signal output by the Mach-Zehnder modulator is transmitted to the transmitting optical antenna. The signal light output by the transmitting optical antenna illuminates the detection target.

[0038] The light signal reflected back by the detected target is received by the receiving optical antenna. The signal output by the receiving optical antenna is used as the input of the photodetector. The radio frequency signal output by the photodetector is used as the input of the second power amplifier. The radio frequency signal is amplified by the second power amplifier and then split into two radio frequency signals.

[0039] Among them, one radio frequency signal output from the second power amplifier and one local oscillation radio frequency signal generated by the second local oscillator are mixed by the third mixer. After mixing, the signal is then passed through the third low-pass filter, the first analog-to-digital converter, and the first digital down-converter in sequence. The other radio frequency signal output from the second power amplifier and another local oscillation radio frequency signal generated by the second local oscillator are mixed by the fourth mixer. After mixing, the signal is then passed through the fourth low-pass filter, the second analog-to-digital converter, and the second digital down-converter in sequence.

[0040] The digital intermediate frequency signal output from the first digital down-converter and the digital intermediate frequency signal output from the second digital down-converter are sent to the computer for processing after passing through the receiver controller and the interface controller. After processing by the computer, the distance and velocity measurement results of the detected target are output.

[0041] Furthermore, the optical signal output by the continuous-wave fiber laser is:

[0042] (1)

[0043] in, and These represent the intensity and angular frequency of the output optical signal from the continuous-wave fiber laser, respectively. The imaginary unit, For time, This represents the optical signal output by a continuous wave fiber laser.

[0044] Furthermore, the optical signal output by the Mach-Zehnder modulator is:

[0045]

[0046] in, This represents the optical signal output by the Mach-Zehnder modulator. This indicates the optical signal in the upper band. This indicates the optical signal in the lower sideband;

[0047]

[0048] Among them, signal amplitude , It is a first-order Bessel function. The normalized amplitude of the radio frequency modulated signal. The phase of the radio frequency modulated signal. For upper band optical signals angular frequency, For the lower sideband optical signal angular frequency;

[0049] Light signal above angular frequency for:

[0050]

[0051] in, Indicates the angular frequency of the radio frequency modulated signal;

[0052] The lower band has optical signal angular frequency for:

[0053]

[0054] Furthermore, the light signal reflected back from the detected target is:

[0055]

[0056]

[0057] in, and Echo optical signal It contains two sideband optical signals. This represents the back-reflected light signal. The intensity of the back-reflected light signal. As the compression factor, This indicates the delay time of the back-reflected light signal. Indicates phase perturbation;

[0058] Compression factor for:

[0059]

[0060] in, At the speed of light, This indicates the radial velocity of the target being detected.

[0061] Furthermore, the method for measuring the distance and velocity of the detected target is as follows:

[0062] Normalized amplitude of microwave radio frequency signal generated by SDR for:

[0063]

[0064] in, For signal time width, It is a rectangular wave. This indicates the voltage amplitude of the pulse linear frequency modulated signal output from the TX terminal;

[0065] Phase of the microwave radio frequency signal generated by SDR for:

[0066]

[0067] in, For linear frequency modulation coefficients, , For frequency modulation bandwidth;

[0068] Computer 7 combines the two received quadrature digital intermediate frequency signals into one complex intermediate frequency signal. Then calculate the complex intermediate frequency signal. The convolution result is obtained by convolving the signal with the unit impulse response of the matched filter. Then based on the convolution results Calculate the distance and velocity of the detected target;

[0069] Unit impulse response of matched filter for:

[0070]

[0071] in, express conjugate, express The reverse fold, This indicates a copy signal stored in the computer;

[0072]

[0073] in, ;

[0074] (1) When the speed of the detected target When less than or equal to 100 m / s:

[0075] Obtain the modulus of the convolution result The time corresponding to the main lobe peak Then the distance to the detected target is:

[0076]

[0077] The target's speed is then calculated based on the results of two consecutive distance measurements. That is, the speed is obtained by dividing the difference between the two measured distances by the time interval between the two measurements. Through multiple measurements, the distance and speed of the detected target can be obtained in real time.

[0078] (2) When the speed of the detected target When the speed is greater than 100m / s:

[0079] The modulus of the convolution result during the first measurement The time corresponding to the main lobe peak is denoted as The magnitude of the convolution result during the second measurement The time corresponding to the main lobe peak is denoted as The speed of the detected target for:

[0080]

[0081] in, Indicates the time interval between the first and second measurements;

[0082] The distance to the detected target for:

[0083]

[0084] in, This indicates the frequency of the signal generated by the second local oscillator.

[0085] Both cases (1) and (2) are applicable The value is relatively small. It should also be noted that when only distance needs to be measured, the first or second option can be selected based on the known target speed.

[0086] Preferably, when only the velocity of the detected target needs to be obtained, the method for measuring the velocity of the detected target is as follows:

[0087] Normalized amplitude of microwave radio frequency signal generated by SDR The digital intermediate frequency signal output by the first digital down-converter is used as the real part of the complex intermediate frequency signal, and the digital intermediate frequency signal output by the second digital down-converter is used as the imaginary part of the complex intermediate frequency signal. That is, the complex intermediate frequency signal is synthesized in the computer based on the digital intermediate frequency signals output by the first and second digital down-converters.

[0088] Perform a Fast Fourier Transform on the complex intermediate frequency (IF) signal to obtain its spectrum; then measure the frequency of the complex IF signal based on its spectrum. And then according to Calculate Doppler frequency shift :

[0089]

[0090] Among them, intermediate variables , , This indicates the angular frequency of the microwave radio frequency signal transmitted by the transmitter.

[0091]

[0092] in, This indicates the carrier frequency of the radio frequency signal output by the photodetector. Indicates the speed of the detected target.

[0093] Preferably, when only the velocity of the detected target needs to be obtained, the method for measuring the velocity of the detected target is as follows:

[0094] Normalized amplitude of microwave radio frequency signal generated by SDR for:

[0095]

[0096] in, For signal time width, It is a rectangular wave. This indicates the voltage amplitude of the pulse linear frequency modulated signal output from the TX terminal;

[0097] Phase of the microwave radio frequency signal generated by SDR for:

[0098]

[0099] in, For linear frequency modulation coefficients, , For frequency modulation bandwidth;

[0100] Computer 7 combines the two received quadrature intermediate frequency (IF) signals into a single complex IF signal. Then calculate the complex intermediate frequency signal. The convolution result is obtained by convolving the signal with the unit impulse response of the matched filter. Then based on the convolution results Calculate the distance and velocity of the detected target;

[0101] Unit impulse response of matched filter for:

[0102]

[0103] in, express conjugate, express The reverse fold, This indicates a copy signal stored in the computer;

[0104]

[0105] in, ;

[0106] Obtain the modulus of the convolution result The time corresponding to the main lobe peak Then the speed of the detected target is:

[0107]

[0108] in, This represents the delay time of the back-reflected light signal, an intermediate variable. , Indicates the linear frequency modulation bandwidth; This indicates the frequency of the signal generated by the second local oscillator, and the frequency of the local oscillator signal. Setting it to a higher value, this speed measurement method is suitable for frequencies. Higher cases.

[0109] The beneficial effects of this invention are:

[0110] This invention proposes an improved direct-detection lidar structure compatible with software-defined radio (SDR). Since the output modulated optical signal of SDR only has two sideband components (no carrier component), a single square-law photodetector is sufficient to demodulate the radio frequency signal from the lidar's echo signal. Compared to existing methods, this invention has a simpler structure and higher power utilization for the back-reflected optical signal. Furthermore, because the frequencies of the transmitted and received microwave radio frequency signals are different, there is no microwave crosstalk between the transmitter and receiver. Because this invention uses a separate transmit / receive optical antenna, there is no need for a fiber optic circulator, thus eliminating crosstalk between optical signals. Without changing the hardware structure, different microwave measurement algorithms can still be implemented through software programming according to detection requirements, achieving different detection functions and measurement indicators. This demonstrates the software-definable nature of detection functions and performance, resulting in higher practicality. Moreover, this invention effectively improves the measurement accuracy of target distance and velocity. When sampling a single-frequency velocimetry algorithm, theory and experiments have shown that it is possible to separately... High-precision measurement of velocity parameters of high-speed targets; the resolution of velocity measurement can reach [resolution missing]. The signal-to-noise ratio (SNR) of pulse-compressed signals depends only on the pulse energy and noise power density, and is independent of the system bandwidth. The SNR can be improved by increasing the energy of the back-reflected signal, thus increasing the signal duration. Compared to traditional pulsed lidar, this reduces the technical requirements for the laser. Theoretical and experimental evidence shows that pulse-compressed signals can be used to measure the distance to stationary targets, achieving a range resolution of up to [insert resolution here]. It can also be used individually. High-precision measurement of velocity parameters of high-speed targets; the resolution of velocity measurement can reach [resolution missing]. . Attached Figure Description

[0111] Figure 1 This is a flowchart of the target range and velocity measurement system based on a direct detection lidar compatible with software radio according to the present invention;

[0112] In the diagram, solid lines represent optical paths, and dashed lines represent electrical circuits.

[0113] Figure 2 These are pulse compression signals from targets at different distances. Detailed Implementation

[0114] Specific Implementation Method 1: Combination Figure 1 This embodiment describes a target range and velocity measurement system based on a direct-detection lidar compatible with software radio. The system comprises two parts: an optical wave path and a radio frequency circuit.

[0115] The optical path includes a continuous wave fiber laser (CWFL) 1, a Mach-Zehnder modulator (MZM) 2, a fiber amplifier (FA) 3, a transmitting optical antenna (TOA) 4, a receiving optical antenna (ROA) 5, and a photodetector (PD) 6; wherein:

[0116] The continuous wave fiber laser 1 is used to generate single-frequency signal light, and the output end of the continuous wave fiber laser 1 is connected to the first input end 2A of the Mach-Zehnder modulator 2.

[0117] The output of the Mach-Zehnder modulator 2 is connected to the input of the fiber amplifier 3.

[0118] The output end of the fiber amplifier 3 is connected to the input end (In end) of the transmitting optical antenna 4, and the signal emitted from the output end (Out end) of the transmitting optical antenna 4 illuminates the detection target.

[0119] The signal reflected back from the target enters the input of the receiving optical antenna 5, and the output of the receiving optical antenna 5 is connected to the input of the photodetector 6.

[0120] The circuitry includes a computer 7 and a software-defined radio (SDR).

[0121] The software-defined radio includes an interface controller 8, a transmit controller 9, a first digital up converter (DUC) 10, a second digital up converter 11, a first digital-to-analog converter (DAC) 12, a second digital-to-analog converter 13, a first low-pass filter (LPF) 14, a second low-pass filter 15, a first local oscillator (LO) 16, a first mixer 17, a second mixer 18, a first power amplifier 19, a second power amplifier 20, a second local oscillator 21, a third mixer 22, a fourth mixer 23, a third low-pass filter 24, a fourth low-pass filter 25, a first analog-to-digital converter (ADC) 26, a second analog-to-digital converter 27, a first digital down converter (DDC) 28, a second digital down converter 29, and a receive controller 30; wherein:

[0122] The output terminal of the computer 7 is connected to the input / output terminal 8A of the interface controller 8;

[0123] The output terminal of the interface controller 8 is connected to the input terminal of the transmission controller 9;

[0124] The first output terminal 9A of the transmitter controller 9 is connected to the input terminal of the first digital up-converter 10; the second output terminal 9B of the transmitter controller 9 is connected to the input terminal of the second digital up-converter 11.

[0125] The output terminal of the first digital-to-digital converter 10 is connected to the input terminal of the first digital-to-analog converter 12; the output terminal of the second digital-to-digital converter 11 is connected to the input terminal of the second digital-to-analog converter 13.

[0126] The output terminal of the first digital-to-analog converter 12 is connected to the input terminal of the first low-pass filter 14; the output terminal of the second digital-to-analog converter 13 is connected to the input terminal of the second low-pass filter 15.

[0127] The first output terminal 16A of the first local oscillator 16 is connected to the first input terminal 17A of the first mixer 17; the second output terminal 16B of the first local oscillator 16 is connected to the first input terminal 18A of the second mixer 18.

[0128] The output terminal of the first low-pass filter 14 is connected to the second input terminal 17B of the first mixer 17; the output terminal of the second low-pass filter 15 is connected to the second input terminal 18B of the second mixer 18.

[0129] The output terminals of the first mixer 17 and the second mixer 18 are connected to the input terminal of the first power amplifier 19.

[0130] The output of the first power amplifier 19 is connected to the second input 2B of the Mach-Zehnder modulator 2;

[0131] The output terminal of the photodetector 6 is connected to the input terminal of the second power amplifier 20;

[0132] The output terminal of the second power amplifier 20 is connected to the first input terminal 22A of the third mixer 22 and the first input terminal 23A of the fourth mixer 23, respectively.

[0133] The first output terminal 21A of the second local oscillator 21 is connected to the second input terminal 22B of the third mixer 22; the second output terminal 21B of the second local oscillator 21 is connected to the second input terminal 23B of the fourth mixer 23.

[0134] The output of the third mixer 22 is connected to the input of the third low-pass filter 24; the output of the fourth mixer 23 is connected to the input of the fourth low-pass filter 25.

[0135] The output of the third low-pass filter 24 is connected to the input of the first analog-to-digital converter 26; the output of the first analog-to-digital converter 26 is connected to the input of the first digital down-converter 28.

[0136] The output of the fourth low-pass filter 25 is connected to the input of the second analog-to-digital converter 27; the output of the second analog-to-digital converter 27 is connected to the input of the second digital down-converter 29.

[0137] The output terminal of the first digital down-converter 28 is connected to the first input terminal 30A of the receiver controller 30; the output terminal of the second digital down-converter 29 is connected to the second input terminal 30B of the receiver controller 30.

[0138] The output terminal of the receiving controller 30 is connected to the input terminal of the interface controller 8, and the interface controller 8 is connected to the input terminal of the computer 7 through the input / output terminal 8A.

[0139] This invention utilizes microwave photonics methods to improve the microwave (RF) modulation and demodulation section of a direct-detection lidar, simplifying its structure, increasing the utilization rate of echo signal optical power, and eliminating crosstalk between microwave (RF) and optical signals. This allows the direct-detection lidar to more efficiently leverage the advantages of microwave (RF) technology, further enhancing its performance in ranging, speed measurement, and other aspects, thus promoting the future development of direct-detection lidar.

[0140] Specific Implementation Method Two: A measurement method for the target range and velocity measurement system based on a direct detection lidar with compatible software radio, as described in Specific Implementation Method One. The measurement method specifically comprises:

[0141] Two orthogonal digital intermediate frequency signals are generated by computer 7. The two orthogonal digital intermediate frequency signals are passed through the interface controller 8 and the transmitter controller 9 of software radio. One signal output from the transmitter controller 9 is then passed through the first digital up-converter 10, the first digital-to-analog converter 12 and the first low-pass filter 14 in sequence. The other signal output from the transmitter controller 9 is passed through the second digital up-converter 11, the second digital-to-analog converter 13 and the second low-pass filter 15 in sequence.

[0142] Two orthogonal analog intermediate frequency signals are output using the first low-pass filter 14 and the second low-pass filter 15.

[0143] Two orthogonal local oscillation radio frequency signals are generated using a first local oscillator 16. The analog intermediate frequency signal output from the first low-pass filter 14 is mixed with one local oscillation radio frequency signal generated by the first local oscillator 16 using a first mixer 17. The analog intermediate frequency signal output from the second low-pass filter 15 is mixed with another local oscillation radio frequency signal generated by the first local oscillator 16 using a second mixer 18 to obtain two mixed radio frequency signals.

[0144] The two mixed radio frequency signals are then combined into one radio frequency signal, and the combined radio frequency signal is amplified by the first power amplifier 19. The amplified signal is then input into the Mach-Zehnder modulator 2.

[0145] The optical signal generated by the continuous wave fiber laser 1 is transmitted to the Mach-Zehnder modulator 2. After the optical signal is amplitude modulated in the Mach-Zehnder modulator 2, the optical signal output by the Mach-Zehnder modulator 2 is transmitted to the transmitting optical antenna 4. The signal light output by the transmitting optical antenna 4 illuminates the detection target.

[0146] The light signal reflected back by the detected target is received by the receiving optical antenna 5. The signal output by the receiving optical antenna 5 is used as the input of the photodetector 6. The radio frequency signal output by the photodetector 6 is used as the input of the second power amplifier 20. The radio frequency signal is amplified by the second power amplifier 20 and then split into two radio frequency signals.

[0147] Specifically, one radio frequency signal output from the second power amplifier 20 and one local oscillation radio frequency signal generated by the second local oscillator 21 are mixed by the third mixer 22. After mixing, the signal passes through the third low-pass filter 24, the first analog-to-digital converter 26, and the first digital down-converter 28 in sequence. The other radio frequency signal output from the second power amplifier 20 and another local oscillation radio frequency signal generated by the second local oscillator 21 are mixed by the fourth mixer 23. After mixing, the signal passes through the fourth low-pass filter 25, the second analog-to-digital converter 27, and the second digital down-converter 29 in sequence.

[0148] The digital intermediate frequency signal output from the first digital down-converter 28 and the digital intermediate frequency signal output from the second digital down-converter 29 are sent to the computer 7 for processing after passing through the receiver controller 30 and the interface controller 8. After processing by the computer 7, the distance and velocity measurement results of the detected target are output.

[0149] like Figure 1 As shown, the circuit enclosed by the dashed line represents Software Defined Radio (SDR). The two orthogonal digital intermediate frequency signals generated by the computer are... and (in, (Representing the sampling point), the signal passes sequentially through the software radio interface controller, transmit controller, digital-to-up converter, digital-to-analog converter, and low-pass filter, becoming two orthogonal analog intermediate frequency signals. and These two analog intermediate frequency signals are respectively orthogonal to two local oscillator microwave (radio frequency) signals. and The mixing process is performed, and the mixing results are combined into a single microwave (radio frequency) signal. Then merge the signals The signal is amplified by a power amplifier and then output from the transmitter. The output microwave (RF) signal is connected to the fiber optic MZM for amplitude modulation of the laser-generated optical signal. The RF signal is generated by the photodetector. After entering the software-defined radio receiver, the signal is amplified by a power amplifier and split into two paths. These two radio frequency (RF) signals are then coupled to two orthogonal local oscillator microwave (RF) signals. and After mixing and passing through a low-pass filter, the signals are converted into two orthogonal analog intermediate frequency signals. and The two orthogonal analog intermediate frequency (IF) signals output from the low-pass filter are then passed through two analog-to-digital converters (ADCs) and a digital down-converter (DPC), respectively, transforming the two analog IF signals into digital IF signals. and The two digital intermediate frequency signals then pass through the receiver controller and interface controller before entering the computer. and To synthesize a complex signal by using the real and imaginary parts respectively. Then, the signal processing algorithm of microwave (radio frequency) radar is used to process the signal to obtain the target's distance. or speed information.

[0150] I. The modulation and demodulation principles of microwaves (radio frequency) are explained in detail below:

[0151] 1. Microwave (radio frequency) modulation of emitted light

[0152] like Figure 1 As shown, the optical signal output by the CWFL is:

[0153] (1)

[0154] in, and These represent the intensity and angular frequency of the output optical signal from the continuous-wave fiber laser, respectively. The imaginary unit, For time;

[0155] After the optical signal output from the CWFL is incident on the MZM, it is split into two paths with identical amplitude and phase by the MZM's own Y-type optocoupler. These paths then pass through two parallel and symmetrical "arms," ​​each of which is a specially designed phase modulator. The modulated electrical signals applied to the two arms of the MZM are as follows:

[0156] (2)

[0157] in, Indicates two different arms. and These are a microwave (radio frequency) modulated signal and a DC bias voltage, respectively; therefore, after phase modulation, these two optical signals become... ;

[0158] in, and These represent the microwave (RF) and DC half-wave voltages of the MZM, respectively. These two optical signals are combined into a single output. Through further processing, the MZM outputs an optical signal. It can be represented as:

[0159] (3)

[0160] According to equation (3), the optical signal after passing through the MZM is simultaneously subjected to amplitude modulation and phase modulation. This causes the frequency of the optical signal to change nonlinearly with time, resulting in different group velocities at different frequencies and generating frequency chirp. To eliminate chirp, the MZM generally operates in push-pull mode, i.e. ,in and Then there is as well as This allows MZM to perform amplitude modulation only, eliminating frequency chirp.

[0161] Assume the phase difference caused by the DC bias voltage of the two arms is In this state, the output optical signal of MZM becomes:

[0162] (4)

[0163] in, It represents a microwave radio frequency modulated signal (i.e., a signal transmitted by the transmitter). This represents the phase difference caused by the DC bias voltage of the two arms;

[0164] When the DC polarization voltage of the two arms is adjusted This results in a fixed phase difference between the two arms. At this time, MZM will operate in minimum transmission point mode, and it is assumed that the microwave modulation signal is hour, , , and These represent the angular frequency, maximum amplitude, normalized amplitude, and phase of the radio frequency modulated signal, respectively. And let... For phase modulation coefficients, , For the maximum phase, Then the output optical signal of the MZM can be expressed as:

[0165] (5)

[0166] For equation (5) The term, expanded using Bessel functions, can be represented as follows: .

[0167] When the range of the phase modulation coefficient is When, then it can be considered that, except for the first-order Bessel function Apart from the term, the values ​​of all other Bessel function terms are approximately zero. It can be approximated as Furthermore, within this interval, the first-order Bessel function Approximately a direct proportional function, that is Therefore, the emitted light signal in formula (5) can be approximately expressed as: Then, using Euler's formula... Term decomposition into The superposition of these two signals results in the final output optical signal of the MZM modulator, which can be expressed as:

[0168] (6)

[0169] in:

[0170] (7)

[0171] By observing formula (6), it can be seen that MZM realizes radio frequency signals. For incident light signals Suppressed carrier double-sideband amplitude modulation. Angular frequencies of the upper and lower sideband optical signals. and Around the frequency of incident light Symmetrical distribution, maximum amplitude and normalized amplitude Same, opposite phase.

[0172] 2. Representation of echo optical signals

[0173] Assume the initial distance between the target and the lidar is... And detect the target at radial velocity Moving towards the lidar, if at the initial distance and the initial echo optical signal delay time For reference (where, If the speed of light is given, then the distance function between the target and the radar can be expressed as:

[0174] (8)

[0175] Therefore, the delay time of the echo optical signal is:

[0176] (9)

[0177] When detecting the radial velocity of the target When, equation (9) becomes , and the distance is Echo signal delay time of stationary target Since they are consistent, formula (9) is correct.

[0178] If the emitted optical signal is as in formula (6) Then the echo signal can be expressed as:

[0179] (10)

[0180] in:

[0181]

[0182] in, and They transmit upper sideband optical signals respectively and transmit lower sideband optical signals The echo optical signal, compression factor , The intensity of the echo signal can be calculated using radar equations.

[0183] Because of the low center frequency, the envelope terms of the upper and lower sidebands of the echo optical signal... and phase term They can be approximated as follows: and Then the echo signal can be written as:

[0184]

[0185] in, ;

[0186] In addition, echo optical signal Two optical signal components and Atmospheric turbulence will affect the phase of both optical signals. and However, since they follow the same path, they experience approximately the same phase perturbation. Therefore, the upper and lower sideband optical signals of the echo optical signal can be rewritten as:

[0187] (11)

[0188] in, This indicates a phase perturbation.

[0189] 3. Radio frequency demodulation of echo optical signals

[0190] The above derivation process illustrates that: (includes...) and Outgoing light signals of two sideband components Irradiation at the initial distance is The initial radial velocity is When the target is reached, the back-reflected light signal Includes two sideband optical signals and Both exhibited frequency changes and time delays. The echo optical signal was incident on a square-law detector, and the output electrical signal... Proportional to light signal The modulus, that is:

[0191] (12)

[0192] By observing equation (12), it can be seen that the output electrical signal Contains DC component and communication components (Depend on and Beat frequency generation), and optical phase disturbance caused by atmospheric turbulence in formula (11). It has been eliminated. The lidar studied in this invention only concerns the AC component of the output electrical signal of the square-law detector. DC component It will be filtered out by the filters of the radio frequency signal processing system. It can be set... The equivalent amplitude of the AC signal. The equivalent angular frequency of the AC signal. If the equivalent phase of the AC signal is given, then the AC component in formula (12) can be written as:

[0193] (13)

[0194] in, Doppler frequency shift of microwave (radio frequency) signals , The phase is constant. .

[0195] If we assume the existence of a microwave (radio frequency) radar, which emits microwave (radio frequency) signals... The initial distance and radial velocity of the irradiated object are the same. and When the target is detected, according to the basic principle of microwave (radio frequency) radar, ignoring amplitude attenuation, the target back-reflected microwave (radio frequency) signal received by the microwave (radio frequency) radar is exactly the same as the demodulated microwave (radio frequency) signal expressed by formula (13): both have undergone [a certain process]. Size of Doppler shift, Size of time delay and The magnitude of the additional phase. Therefore, the signal processing method of microwave (RF) radar can be directly used to process formula (13) by measuring the Doppler frequency shift of the microwave. and time delay The radial velocity of the target can be obtained. and distance This information allows the advantages of microwave (radio frequency) radar to be seamlessly transferred to lidar.

[0196] Furthermore, lidar employing this microwave (radio frequency) modulation and demodulation technology, besides possessing the characteristics of resistance to atmospheric turbulence and the ability to leverage the advantages of microwave (radio frequency) radar technology, also precisely meets the technical requirements of frequency division duplexing (FDD) in microwave (radio frequency) communication systems, effectively reducing radio frequency crosstalk at the transmitting and receiving ends. Figure 1 The center frequency of the signal received by the microwave device With the center frequency of the transmitted signal different.

[0197] II. Methods for measuring the speed and distance of a target

[0198] The direct detection lidar proposed in this invention utilizes the demodulated microwave (radio frequency) signal, which is identical to the echo signal from the microwave (radio frequency) radar in formula (13), for target measurement. Theoretically, any advanced measurement method for microwave radar can be used. This invention combines... Figure 1 To verify the performance of the SDR (Self-Driving Radar) device in the microwave (RF) system, two typical microwave (RF) radar measurement methods were selected to demonstrate the correctness of this lidar theory. The specific microwave (RF) radar measurement methods are as follows:

[0199] 1. Single-frequency microwave (radio frequency) signal speed measurement method

[0200] By programming the SDR, the normalized amplitude and phase of the generated analog intermediate frequency signal are respectively... and And set the frequency of the quadrature local oscillator signal at the TX terminal to be After power amplification, the microwave (radio frequency) signal output at the TX terminal is This generates a continuous single-frequency microwave (radio frequency) signal. Assume the target's velocity and distance are respectively... and According to formula (13), the microwave (radio frequency) signal output from the photodetector PD is proportional to... ,in , , , .

[0201] Furthermore, by programming the SDR, the frequency of the local oscillator microwave (RF) signal at the RX terminal is set to... This generates two orthogonal local oscillator signals. and The signal is then sequentially mixed with the output signal from the photodetector entering the RX terminal. After low-pass filtering, the mixed signal generates two orthogonal intermediate frequency signals. and , where constant .

[0202] After being sampled by an analog-to-digital converter (ADC), the signals are input into a computer, where the two acquired digital intermediate frequency (IF) signals are used as the real and imaginary parts, respectively, to construct a complex IF signal. ,in, The sampling frequency of the ADC and the angular frequency of the digital intermediate frequency signal output by the digital down-converter. Doppler frequency shift , for Integers within a range This represents the total number of sampling points.

[0203] In a computer, a program is used to process complex intermediate frequency signals. Perform a Fast Fourier Transform (FFT) to obtain its spectral density. ( (where the integer is an integer), the complex intermediate frequency signal can be measured through the spectrum. angular frequency This allows us to obtain the Doppler frequency shift. And use the Doppler frequency shift to obtain the target's velocity:

[0204] (14)

[0205] Due to the sampling frequency of the ADC The complex intermediate frequency signal is determined FFT spectrum The frequency range, therefore the frequency measurement value of the complex intermediate frequency signal should be within the range of... If the range is specified, then the Doppler frequency shift measurement range is... This results in the target velocity measurement range being:

[0206] (15)

[0207] Number of sampling points Determines the spectrum Independent variable The range of values Therefore, the spectrum The frequency resolution is ,in, This represents the sampling time or the duration of the signal.

[0208] Therefore, the resolution of the Doppler frequency shift is This results in the target velocity measurement resolution being:

[0209] (16)

[0210] 2. Methods for measuring pulse compression distance and velocity

[0211] By programming the SDR, the SDR generates normalized amplitude and phase respectively. and The analog intermediate frequency signal, in which, For signal time width, For linear frequency modulation coefficients, , For frequency modulation bandwidth, It is a rectangular wave. This indicates the voltage amplitude of the pulsed linear frequency modulated signal output from the TX terminal, and sets the frequency of the transmitted local oscillator signal to be [value missing]. After power amplification, a pulse linear frequency modulated signal is output at the TX terminal. Assuming the target's radial velocity and distance remain the same... and According to formula (13), the microwave (radio frequency) signal output from the photodetector PD is proportional to... ;

[0212] in, , , , And its linear frequency modulation bandwidth is Furthermore, the frequency of the local oscillator signal at the receiving end is set by programming the SDR. So that the two quadrature local oscillator signals generated by the local oscillator are respectively and The two orthogonal local oscillator signals are sequentially mixed with and low-pass filtered by the photodetector output signal to generate two orthogonal intermediate frequency signals, namely:

[0213]

[0214]

[0215] The two orthogonal intermediate frequency (IF) signals are then sampled by an analog-to-digital converter (ADC) and fed into a computer. The computer then uses the two acquired digital IF signals as the real and imaginary parts of a complex IF signal, respectively, to construct the complex IF signal. (For the sake of convenience in the subsequent formula derivation, we will temporarily use continuous time variables here.) (Describe the complex intermediate frequency signal):

[0216] (17)

[0217] In the presence of additive noise, to obtain the maximum signal-to-noise ratio, the received signal can be... After passing through an optimal filter that matches it, that is, allowing the received signal to... After passing through a matched filter, the unit impulse response of the matched filter is: ,in, For a copy of the signal stored in the computer, .

[0218] The output of the matched filter This can be represented as a received signal. With unit impulse response The convolution, i.e.:

[0219] (18)

[0220] Equation (18) illustrates that, after further derivation, the output of the matched filter... It can be simplified to receiving signals. With replica signal The relevant operations are therefore:

[0221] (19)

[0222] If we set and ,but Then equation (19) becomes:

[0223] (20)

[0224] Among them, Doppler frequency shift In microwave (radio frequency) radar signal processing, The fuzzy function is It can be used to analyze some properties of received signal pulses after passing through a matched filter.

[0225] For fuzzy functions After sorting, we get:

[0226] (twenty one)

[0227] ①When At that time, Within the range ,so .

[0228] ②When At that time, Within the range Therefore, formula (17) becomes:

[0229] (twenty two)

[0230] ③When At that time, Within the range Therefore, formula (17) becomes:

[0231] (twenty three)

[0232] Combining the above three cases, we get:

[0233]

[0234] After calculation Then, Substitute into From Then Substituting into equation (20), we obtain the specific expression for the output signal:

[0235] (twenty four)

[0236] Among them, the frequency of receiving the local oscillator signal The equivalent angular frequency of an AC signal , The angular frequency of the radio frequency modulated signal, and the Doppler frequency shift. Doppler frequency shift of microwave (radio frequency) signals , At the speed of light, The delay time of the echo signal. The duration of the echo signal is an intermediate variable. , Indicates the linear frequency modulation bandwidth;

[0237] In actual measurements, we are more concerned with the modulus of the output complex signal, so we take the modulus of equation (24):

[0238] (25)

[0239] Analysis of equation (25) shows that the output signal modulus In essence is Function. Due to The peak position of the main lobe is The peak height of the main lobe is 1, and the equivalent width of the main lobe is... Therefore, it can be derived from... get The peak position of the main lobe is .because With delay time and Doppler shift It changes with the changes, so it can be utilized Distance to the target being detected or speed Perform measurements. Determine the position of the main lobe peak. Substitution It can be obtained The height of the main lobe peak is Its value determines the signal-to-noise ratio.

[0240] With other conditions remaining unchanged, as the signal duration... The increase, main lobe peak height This will increase, thus increasing the signal-to-noise ratio; with Doppler frequency shift... The increase, main lobe peak height This will decrease, thus reducing the signal-to-noise ratio. (This can be achieved by...) get The position of the first zero point to the right of the main lobe peak Thus, one can obtain Equivalent width of the main lobe And because Compared to It is relatively small, so it can be ignored. The equivalent width of the main lobe is approximately: With other conditions remaining unchanged, as the modulation bandwidth... The increase, Equivalent width of the main lobe peak It will decrease as the echo signal undergoes a Doppler frequency shift. The increase in the width of the main lobe peak increases. It will increase.

[0241] From the above, we can see that the time width is... echo signal The modulus of the output signal after the matched filter The main lobe equivalent time width is reduced to In other words, the time span was compressed. Therefore, the output signal is times greater. It can also be called a pulse compression signal, usually Also known as the time-width-bandwidth product. Pulse compression signal mode The equivalent time width of the main lobe peak determines the minimum distance between two resolvable adjacent peaks, which is the peak measurement resolution. The smaller the value, the stronger the radar's resolution. Therefore, The delay time is determined by itself. Measurement resolution, Determines the Doppler frequency shift The measurement resolution.

[0242] According to matched filter theory, the modulus of its output pulse compression signal is... The signal-to-noise ratio is:

[0243] (26)

[0244] in, The time width is echo signal pulse energy, To detect the equivalent noise power spectral density of the system, the division by 2 indicates that a double-sideband spectrum representation is used. In other words, the output signal-to-noise ratio of the matched filter depends on the energy of the input pulse signal and the noise power spectral density, and is independent of the waveform of the input signal and the system bandwidth.

[0245] The echo signal input to the matched filter In its bandwidth The noise power inside is echo signal The average power is Therefore, the input signal-to-noise ratio of the matched filter is:

[0246] (27)

[0247] Therefore, after pulse compression via a matched filter, the signal-to-noise ratio of the echo signal is improved. The difference is several times greater. For traditional pulse ranging lidar, since matched filtering is not used to compress the echo signal, under the same conditions, achieving the same resolution and signal-to-noise ratio as the method of this invention requires a much narrower emission time width (narrower). (times) and higher peak power (high) The high pulse power (times) of lasers places extremely stringent technical requirements on lasers, making it difficult to improve their performance through further enhancements. However, the direct-detection lidar structure proposed in this invention does not require the emission of extremely narrow pulse widths and extremely high peak power laser pulses, resulting in much lower technical requirements for the laser. Therefore, there is still significant potential to further improve the performance of direct-detection lidars by enhancing laser performance in the future.

[0248] (1) Utilizing the mode of pulse compression signal Perform distance measurement

[0249] The frequency of the local oscillator signal at the software radio SDR receiver (RX end) (or Set to a lower value ( ), and when the speed of the detected target At relatively low speeds (below 100 m / s), this causes a Doppler frequency shift. Caused shift of compression peak Less than peak measurement resolution At that time, the peak position of pulse compression Only related to signal delay time Related, that is Then, the distance to the target can be measured separately using the compressed peak:

[0250] (28)

[0251] in, The magnitude of the convolution result The position of the main lobe peak;

[0252] Time delay Measurement resolution This is equivalent to the resolution of the pulse compression peak. ,Right now Therefore, the distance measurement resolution is:

[0253] (29)

[0254] To avoid distance ambiguity, a time delay is required. Therefore, the maximum delay time is Therefore, the maximum measurable distance is:

[0255] (30)

[0256] Due to the height of the pulse compression peak Unaffected by Doppler frequency shift The signal-to-noise ratio remains unchanged due to the influence of the distance measurement method in formula (28). The velocity of the target can also be calculated from the two distance measurements.

[0257] When the target speed At very high speeds, such as several Mach, even if the frequency of the local oscillator signal at the SDR receiver (RX end) is set... (or () is the minimum value It also cannot shift the compression peak caused by Doppler frequency shift. Less than peak measurement resolution The position of the pulse compression peak It will deviate from the delay time Location, there exists a The magnitude of the deviation. In this case, it can be determined by measuring the positions of two consecutive pulse compression peaks. and Correct the distance measurement value and obtain the target's speed at the same time.

[0258] Assuming the time interval between two peak position measurements Given a known value, and because Since the value is small, it can be assumed that the target's velocity remains constant between the two measurements. and If the value is constant, then two measurement equations can be written:

[0259] (31)

[0260] in, and The distances to the target during the first and second measurements, respectively. and The resulting time delay, , .

[0261] Subtracting the two equations in formula (31) yields the following result. (Doppler frequency shift term) (was eliminated), and because Therefore, the target's velocity can be calculated:

[0262] (32)

[0263] Furthermore, the speed measurement value in the above formula can be used. The corresponding Doppler frequency shift was calculated as follows: .

[0264] Adding the two equations in formula (31) gives us The average of the two initial distances and Doppler frequency shift measurements Substituting these values ​​into the equation, we can obtain the correction value for the distance measurement:

[0265] (33)

[0266] This utilizes the measured values ​​of the compression peak positions of two adjacent pulses. and A set of distance and speed measurements can be obtained. and If another time interval is passed... The position of the third pulse compression peak was measured. Then the same method as above can be used to utilize... and Obtain the second set of distance and speed measurements. and If according to the known time interval , obtain in sequence pulse compression peak position value The measured values ​​can be obtained sequentially using the method described above. Measurements of the distance and speed of the group of targets.

[0267] This method of measuring target distance using pulse compression peaks requires only a low-bandwidth photodetector, whose bandwidth is approximately equal to the linear frequency modulation bandwidth. Therefore, it is not necessary to use a high-bandwidth photodetector; the space photodetector used in traditional pulse ranging lidar can be used instead, which can achieve higher optical efficiency.

[0268] (2) Utilizing the modulus of pulse compression signals Speed ​​measurement alone

[0269] The frequency of the local oscillator signal at the software radio SDR receiver (RX end) (or Set it to a high value (in the order of several GHz) to achieve the same speed. Caused Doppler frequency shift The larger the distance, the easier it is to measure. And when the target distance... When the delay time is a known constant, Since the value is a known constant, the position of the pulse compression peak can be used. The only indication of Doppler frequency shift Thus, the position of the compression peak can be used alone. Perform velocity measurement of the detected target:

[0270] (34)

[0271] Doppler frequency shift Differentiating both sides and taking the absolute value, we have If Measure resolution using peak value Instead, Measure resolution using frequency shift Instead, the frequency shift measurement resolution is (This is the same resolution as the Doppler frequency shift measurement in the previous single-frequency signal test.)

[0272] Therefore, the speed measurement resolution is:

[0273] (35)

[0274] In addition, the height of the pulse compression peak The height of the pulse compression peak will change with the Doppler frequency shift. As it increases, it decreases. At this time, the height of the pulse compression peak reaches its maximum, that is... ,exist At this time, the height of the pulse compression peak reaches its minimum, that is If we assume the maximum permissible Doppler frequency shift... Reduce the height of the pulse compression peak to ( ,For example ),but ,Right now Then the maximum measurable speed is:

[0275] (36)

[0276] III. Experimental Section

[0277] To experimentally verify the method proposed in this invention, we built... Figure 1 The experimental setup shown uses a WIN LIGHT WL-1550B10-APC fiber laser module in its optical path, with an output power of approximately 10mW, a wavelength of approximately 1550nm, and a linewidth of approximately [missing information]. The single-frequency continuous laser light, after passing through an iXblue MXER-LN-10 high extinction ratio fiber intensity modulator with a maximum modulation bandwidth of 10 GHz, is then amplified by an OPEAK EFDFA-MC-CW-30-S continuous fiber amplifier module (whose maximum output power is approximately...). The light is amplified and then collimated into parallel light by a Thorlab TC25APC-1550 fiber optic beam expander and collimator before being output and illuminating a target with a reflective strip on its surface. The back-reflected signal light from the target is collected by a similar beam expander and collimator and then detected by a Newport 1414 photodetector, which outputs an RF signal. The circuitry uses a YunSDR Y590neo software radio module manufactured by Beijing Weishuiri Technology Co., Ltd. This module has four RF signal transmitters (TX) and four RF signal receivers (RX). The RF signal generated by one transmitter is modulated by an intensity modulator and applied to the emitted laser, while the RF receiver receives the RF signal output from the photodetector. The SDR module's RF signal frequency range is 75MHz to 6GHz, with a maximum sampling rate of 245.76MHz and a maximum system bandwidth of 200MHz. The module connects to a PC via a high-speed 40G SFP+ interface for data stream transmission. The generation, reception, and processing of radio frequency signals by this software radio module are all controlled by a user program on a PC.

[0278] Experimental Results and Analysis of Target Distance Measurement Using Pulse Compression Method

[0279] use Figure 1 The experimental setup shown emits a laser towards a fixed target with reflective strips attached to its surface, and the carrier frequency of the emitted radio frequency signal is... Linear frequency modulation bandwidth Pulse duration The carrier frequency of the radio frequency signal demodulated from the back-reflected signal light. Linear frequency modulation bandwidth Pulse duration After performing quadrature mixing to convert it into an intermediate frequency signal, it is then frequency-controlled. The signal is sampled and processed according to formula (18) to obtain a pulse compression signal. The peak position of the pulse compression signal is defined as... ,like Figure 2 The solid line indicates that this position is defined as the reference position. With other conditions remaining unchanged, an extension of approximately [length missing] is inserted between the receiving optical antenna and the photoelectric detector. , and The length of the delay fiber, since the refractive index of the fiber is approximately This can be equivalent to moving the target from the reference position sequentially by approximately , and And respectively, measurements were performed to obtain the corresponding pulse compression signals, and in Figure 2The lines are represented using dashed lines, dotted lines, and dashed-dot lines, respectively. Through observation... Figure 2 It can be seen that the peak positions of these three pulse compression signals are respectively , and Then the equivalent relative distance measurement can be obtained. Compared with the true value The deviations are respectively , and All are less than the distance resolution in formula (29). Therefore, the correctness of the method of the present invention can be proven.

Claims

1. A target range and velocity measurement system based on a direct-detection lidar compatible with software-defined radio, characterized in that, The system comprises two parts: an optical path and a circuit. The optical path includes a continuous-wave fiber laser (1), a Mach-Zehnder modulator (2), a fiber amplifier (3), a transmitting optical antenna (4), a receiving optical antenna (5), and a photodetector (6); wherein: The continuous wave fiber laser (1) is used to generate single-frequency signal light, and the output end of the continuous wave fiber laser (1) is connected to the first input end (2A) of the Mach-Zehnder modulator (2). The output of the Mach-Zehnder modulator (2) is connected to the input of the fiber amplifier (3); The output end of the fiber amplifier (3) is connected to the input end of the transmitting optical antenna (4), and the signal emitted from the output end of the transmitting optical antenna (4) illuminates the detection target. The signal reflected back from the target enters the input end of the receiving optical antenna (5), and the output end of the receiving optical antenna (5) is connected to the input end of the photodetector (6); The circuitry includes a computer (7) and a software-defined radio; The software-defined radio includes an interface controller (8), a transmit controller (9), a first digital up-converter (10), a second digital up-converter (11), a first digital-to-analog converter (12), a second digital-to-analog converter (13), a first low-pass filter (14), a second low-pass filter (15), a first local oscillator (16), a first mixer (17), a second mixer (18), a first power amplifier (19), a second power amplifier (20), a second local oscillator (21), a third mixer (22), a fourth mixer (23), a third low-pass filter (24), a fourth low-pass filter (25), a first analog-to-digital converter (26), a second analog-to-digital converter (27), a first digital down-converter (28), a second digital down-converter (29), and a receive controller (30); wherein: The output terminal of the computer (7) is connected to the input / output terminal (8A) of the interface controller (8); The output terminal of the interface controller (8) is connected to the input terminal of the transmission controller (9); The first output terminal (9A) of the transmitter controller (9) is connected to the input terminal of the first digital up-converter (10); the second output terminal (9B) of the transmitter controller (9) is connected to the input terminal of the second digital up-converter (11); The output of the first digital-to-digital converter (10) is connected to the input of the first digital-to-analog converter (12); the output of the second digital-to-digital converter (11) is connected to the input of the second digital-to-analog converter (13); The output of the first digital-to-analog converter (12) is connected to the input of the first low-pass filter (14); the output of the second digital-to-analog converter (13) is connected to the input of the second low-pass filter (15); The first output terminal (16A) of the first local oscillator (16) is connected to the first input terminal (17A) of the first mixer (17); the second output terminal (16B) of the first local oscillator (16) is connected to the first input terminal (18A) of the second mixer (18); The output of the first low-pass filter (14) is connected to the second input (17B) of the first mixer (17); the output of the second low-pass filter (15) is connected to the second input (18B) of the second mixer (18); The output terminals of the first mixer (17) and the second mixer (18) are connected to the input terminal of the first power amplifier (19); The output of the first power amplifier (19) is connected to the second input (2B) of the Mach-Zehnder modulator (2); The output terminal of the photodetector (6) is connected to the input terminal of the second power amplifier (20); The output terminal of the second power amplifier (20) is connected to the first input terminal (22A) of the third mixer (22) and the first input terminal (23A) of the fourth mixer (23), respectively; The first output terminal (21A) of the second local oscillator (21) is connected to the second input terminal (22B) of the third mixer (22); the second output terminal (21B) of the second local oscillator (21) is connected to the second input terminal (23B) of the fourth mixer (23); The output of the third mixer (22) is connected to the input of the third low-pass filter (24); the output of the fourth mixer (23) is connected to the input of the fourth low-pass filter (25). The output of the third low-pass filter (24) is connected to the input of the first analog-to-digital converter (26); the output of the first analog-to-digital converter (26) is connected to the input of the first digital down-converter (28); The output of the fourth low-pass filter (25) is connected to the input of the second analog-to-digital converter (27); the output of the second analog-to-digital converter (27) is connected to the input of the second digital down-converter (29); The output of the first digital down-converter (28) is connected to the first input (30A) of the receiver controller (30); the output of the second digital down-converter (29) is connected to the second input (30B) of the receiver controller (30); The output of the receiving controller (30) is connected to the input of the interface controller (8), and the interface controller (8) is connected to the input of the computer (7) through the input / output terminal (8A).

2. The measurement method for the target range and velocity measurement system based on a direct detection lidar with compatible software radio as described in claim 1, characterized in that, The measurement method is specifically as follows: Two orthogonal digital intermediate frequency signals are generated by computer (7). The two orthogonal digital intermediate frequency signals are passed through the interface controller (8) and the transmitter controller (9) of software radio. Then, one signal output by the transmitter controller (9) is passed through the first digital up-converter (10), the first digital-to-analog converter (12) and the first low-pass filter (14) in sequence. The other signal output by the transmitter controller (9) is passed through the second digital up-converter (11), the second digital-to-analog converter (13) and the second low-pass filter (15) in sequence. Two orthogonal analog intermediate frequency signals are output using the first low-pass filter (14) and the second low-pass filter (15); Two orthogonal local oscillation radio frequency signals are generated using a first local oscillator (16). The analog intermediate frequency signal output from the first low-pass filter (14) is mixed with one local oscillation radio frequency signal generated by the first local oscillator (16) using a first mixer (17). The analog intermediate frequency signal output from the second low-pass filter (15) is mixed with another local oscillation radio frequency signal generated by the first local oscillator (16) using a second mixer (18) to obtain two mixed radio frequency signals. The two mixed radio frequency signals are then combined into one radio frequency signal, and the combined radio frequency signal is amplified by the first power amplifier (19), and the amplified signal is input into the Mach-Zehnder modulator (2). The optical signal generated by the continuous wave fiber laser (1) is transmitted to the Mach-Zehnder modulator (2). After the optical signal is amplitude modulated in the Mach-Zehnder modulator (2), the optical signal output by the Mach-Zehnder modulator (2) is transmitted to the transmitting optical antenna (4). The signal light output by the transmitting optical antenna (4) illuminates the detection target. The light signal reflected back by the detected target is received by the receiving optical antenna (5). The signal output by the receiving optical antenna (5) is used as the input of the photodetector (6). The radio frequency signal output by the photodetector (6) is used as the input of the second power amplifier (20). The radio frequency signal is amplified by the second power amplifier (20) and then split into two radio frequency signals. Among them, one radio frequency signal output from the second power amplifier (20) and one local oscillation radio frequency signal generated by the second local oscillator (21) are mixed by the third mixer (22), and the mixed signal then passes through the third low-pass filter (24), the first analog-to-digital converter (26) and the first digital down-converter (28) in sequence; another radio frequency signal output from the second power amplifier (20) and another local oscillation radio frequency signal generated by the second local oscillator (21) are mixed by the fourth mixer (23), and the mixed signal then passes through the fourth low-pass filter (25), the second analog-to-digital converter (27) and the second digital down-converter (29) in sequence. The digital intermediate frequency signal output by the first digital down-converter (28) and the digital intermediate frequency signal output by the second digital down-converter (29) are sent to the computer (7) for processing after passing through the receiver controller (30) and the interface controller (8). After processing by the computer (7), the distance and speed measurement results of the target are output.

3. The measurement method for the target range and velocity measurement system based on a direct detection lidar compatible with software radio as described in claim 2, characterized in that, The optical signal output by the continuous wave fiber laser is: in, and These represent the intensity and angular frequency of the output optical signal from the continuous-wave fiber laser, respectively. The imaginary unit, For time, This represents the optical signal output by a continuous wave fiber laser.

4. The measurement method for the target range and velocity measurement system based on a direct detection lidar compatible with software radio as described in claim 3, characterized in that, The optical signal output by the Mach-Zehnder modulator is: in, This represents the optical signal output by the Mach-Zehnder modulator. This indicates the optical signal in the upper band. This indicates the optical signal in the lower sideband; Among them, signal amplitude , It is a first-order Bessel function. The normalized amplitude of the radio frequency modulated signal. The phase of the radio frequency modulated signal. For upper band optical signals angular frequency, For the lower sideband optical signal angular frequency.

5. The measurement method for the target range and velocity measurement system based on a direct detection lidar compatible with software radio according to claim 4, characterized in that, The upper sideband optical signal angular frequency for: in, This indicates the angular frequency of the radio frequency modulated signal.

6. The measurement method for the target range and velocity measurement system based on a software-compatible direct detection lidar according to claim 5, characterized in that, The lower sideband optical signal angular frequency for: 。 7. The measurement method for the target range and velocity measurement system based on a direct detection lidar with compatible software radio as described in claim 6, characterized in that, The light signal reflected back from the detected target is: in, and Echo optical signal It contains two sideband optical signals. This represents the back-reflected light signal. The intensity of the back-reflected light signal. The compression factor, This indicates the delay time of the back-reflected light signal. Indicates phase perturbation; Compression factor for: in, At the speed of light, This indicates the radial velocity of the target being detected.

8. The measurement method for the target range and velocity measurement system based on a direct detection lidar with compatible software radio as described in claim 7, characterized in that, The method for measuring the distance and velocity of the detected target is as follows: Normalized amplitude of microwave radio frequency signal generated by SDR for: in, For signal time width, It is a rectangular wave. This indicates the voltage amplitude of the pulse linear frequency modulated signal output from the TX terminal; Phase of the microwave radio frequency signal generated by SDR for: in, For linear frequency modulation coefficients, , For frequency modulation bandwidth; The computer (7) combines the two received quadrature digital intermediate frequency signals into one complex intermediate frequency signal. Then calculate the complex intermediate frequency signal. The convolution result is obtained by convolving the signal with the unit impulse response of the matched filter. Then based on the convolution results Calculate the distance and velocity of the detected target; Unit impulse response of matched filter for: in, express conjugate, express The reverse fold, This indicates a copy signal stored in the computer; in, ; (1) When the speed of the detected target When less than or equal to 100 m / s: Obtain the modulus of the convolution result The time corresponding to the main lobe peak Then the distance to the detected target is: Then, calculate the target's velocity based on the results of two consecutive distance measurements; (2) When the speed of the detected target When the speed is greater than 100m / s: The modulus of the convolution result during the first measurement The time corresponding to the main lobe peak is denoted as The magnitude of the convolution result during the second measurement The time corresponding to the main lobe peak is denoted as The speed of the detected target for: in, Indicates the time interval between the first and second measurements; Then the distance of the detected target for: in, This indicates the frequency of the signal generated by the second local oscillator.

9. The measurement method for the target range and velocity measurement system based on a direct detection lidar with compatible software radio as described in claim 7, characterized in that, When only the velocity of the target needs to be obtained, the method for measuring the target velocity is as follows: Normalized amplitude of microwave radio frequency signal generated by SDR The digital intermediate frequency signal output by the first digital down-converter is used as the real part of the complex intermediate frequency signal, and the digital intermediate frequency signal output by the second digital down-converter is used as the imaginary part of the complex intermediate frequency signal. That is, the complex intermediate frequency signal is synthesized in the computer based on the digital intermediate frequency signals output by the first and second digital down-converters. Perform a Fast Fourier Transform on the complex intermediate frequency (IF) signal to obtain its spectrum; then measure the frequency of the complex IF signal based on its spectrum. And then according to Calculate Doppler frequency shift : Among them, intermediate variables , , This indicates the angular frequency of the microwave radio frequency signal transmitted by the transmitter. in, This indicates the carrier frequency of the radio frequency signal output by the photodetector. Indicates the speed of the detected target.

10. The measurement method for the target range and velocity measurement system based on a software-compatible direct detection lidar according to claim 7, characterized in that, When only the velocity of the target needs to be obtained, the method for measuring the target velocity is as follows: Normalized amplitude of microwave radio frequency signal generated by SDR for: in, For signal time width, It is a rectangular wave. This indicates the voltage amplitude of the pulse linear frequency modulated signal output from the TX terminal; Phase of the microwave radio frequency signal generated by SDR for: in, For linear frequency modulation coefficients, , For frequency modulation bandwidth; The computer (7) combines the two received quadrature intermediate frequency signals into one complex intermediate frequency signal. Then calculate the complex intermediate frequency signal. The convolution result is obtained by convolving the signal with the unit impulse response of the matched filter. Then based on the convolution results Calculate the distance and velocity of the detected target; Unit impulse response of matched filter for: in, express conjugate, express The reverse fold, This indicates a copy signal stored in the computer; in, ; Obtain the modulus of the convolution result The time corresponding to the main lobe peak Then the speed of the detected target is: in, This indicates the frequency of the signal generated by the second local oscillator. , This indicates the delay time of the back-reflected signal light.

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