A method and apparatus for ranging, velocity measurement and imaging based on combined coding

Abstract

This invention discloses a ranging, velocimetry, and imaging method and apparatus based on combined coding. The apparatus includes: a laser, a coded signal generator, an optical phase modulator, an optical amplifier, an optical transceiver system, an optical demodulator, a photodetector, an analog-to-digital converter, and a signal processor. The method utilizes the apparatus to concatenate several different coded sequences into a single combined code to modulate the laser, leveraging the characteristics of each coded sequence during transmission to achieve corresponding functions. This invention effectively acquires and compensates for target Doppler information without requiring additional equipment, solving the problems of low Doppler tolerance and limited applicability of traditional phase-coded lidar. Furthermore, by embedding information coding segments, information transmission can be achieved, improving the anti-interference capability between radars.

Description

Technical Field

[0001] This invention belongs to the field of lidar and is mainly used for radar ranging and velocity measurement and super-resolution imaging of long-range targets. Background Technology

[0002] LiDAR is an important modern ranging and velocity measurement sensor, and coherent lidar, with its advantages of high detection sensitivity and flexible modulation, is one of the important development directions of lidar. Currently, coherent lidar mainly adopts the relatively mature FMCW scheme. Phase coding schemes, due to their advantages such as low linearity requirements, absence of range-Doppler coupling, high amplifier efficiency, strong anti-interception capability, and diverse waveform designs, are also under research. Phase coding is a Doppler-sensitive signal; as the echo Doppler frequency shift increases, the detection capability decreases sharply, thus it is only suitable for stationary or low-speed moving targets. With the increasing number of lidars in use, higher requirements are placed on the ability to combat inter-radar crosstalk; in application scenarios requiring multi-machine collaboration, the information interconnection capability between radars is also particularly important.

[0003] One prior art technique (see Xuesong Mao, Daisuke Inoue, Hiroyuki Matsubara, and Manabu Kagami, Demonstration of in-car doppler laser radar at 1.55µm for range and speed measurement, IEEE Transactions on Intelligent Transportation Systems, 2013, Vol. 14, No. 2, 599-607) inserts a periodic code into a pseudo-random code to form a modulation code. While using correlation operations to obtain target range information, the Doppler frequency is analyzed by sampling the heterodyne signal of the periodic code. However, inserting a periodic code into the pseudo-random code reduces its autocorrelation characteristics, and the speed measurement range is limited.

[0004] In the second prior art (see Wang Yanfei, Fan Bangkui, Li Heping, Han Song. A method and system for simultaneous imaging and detection based on coded array. CN114236491A[P]. 2022-03-25.), each element in the radar array is assigned a separable, individual signal. After receiving the echo signal, each element performs separate processing, allowing for flexible adjustment of imaging performance and moving target detection performance. This system requires N radar radiation elements, N coded signals, N transmitters and receivers, and N data acquisition units to transmit N orthogonal signals, making the system complex and costly.

[0005] In the third prior art (see Gao Fengli, Li Sida, Tao Min, et al. A system and method for simultaneously realizing laser ranging and communication. CN112953645B[P]. 2023-02-28.), a method based on dual-pulse interval modulation is used, where the duration between pulses represents logic 0 and 1, and the time of flight of the echo is used for ranging. This ranging and communication method has poor anti-interference capabilities. In multi-radar operating scenarios, if the receiver acquires data from two or more different radars in a short period of time, it can only discard the acquired signal as invalid data, resulting in poor working efficiency.

[0006] In summary, current phase-coded lidar systems offer various trade-offs in terms of detection capability, system complexity, and anti-interference capabilities when implementing ranging, velocity measurement, Doppler compensation, imaging, and communication. Summary of the Invention

[0007] This invention provides a ranging, velocimetry, and imaging method and apparatus based on combined coding to overcome the problem of limited application range caused by the low Doppler tolerance of existing phase-coded coherent lidar; in addition, it also improves the ability to resist inter-radar crosstalk.

[0008] The technical solution provided by this invention is as follows:

[0009] A ranging, velocimetry, and imaging method based on combined coding, which mainly includes the following steps:

[0010] S1: Generate a combined code as a driving signal to modulate the laser;

[0011] S2: Output a modulated laser signal, and the modulated laser signal illuminates the target under test and generates backscattered light; extract the echo signal from the backscattered light, use the strongest single-frequency component in the echo signal as the target radial Doppler to complete the velocity measurement, and compensate for the target radial Doppler through signal processing;

[0012] S3: Use a matched filter to obtain target distance information from the echo signal, and at the same time determine the starting point of each combination code in the target distance information data to rearrange the echo signal into a data matrix;

[0013] S4: Based on prior information about the combined coding distribution, the data matrix is ​​divided into different sub-matrices;

[0014] S5: Use the synthetic aperture imaging algorithm to achieve super-resolution imaging on the radar data submatrix in the submatrix, and perform key decoding after carrier recovery on the local information submatrix in the submatrix to obtain information.

[0015] Furthermore, the radar data segment in the combined encoding has a length of N, and both ends have a 0 value interval with a length not less than N / 2; the radar data sub-matrix is ​​composed of multiple pulses of the radar data segment.

[0016] Furthermore, the 0-value interval has a certain proportion in the combined coding, so that the spectral intensity of the single-frequency signal is higher than that of the broadband region, thereby accurately extracting and compensating for the target radial Doppler.

[0017] Furthermore, the combined encoding embeds a signal modulated with orthogonal codes as the key, and information is obtained by decoding the key, thereby enabling local information interconnection between radars.

[0018] Furthermore, the combined encoding embeds a local identifier.

[0019] On the other hand, the present invention also provides a ranging, velocimetry, and imaging device based on combined coding, the device comprising: a laser, a coded signal generator, an optical phase modulator, an optical amplifier, an optical transceiver system, an optical demodulator, a photodetector, an analog-to-digital converter, and a signal processor, wherein...

[0020] The laser outputs two signals: one is a local oscillator signal, and the other is a signal to be modulated. The local oscillator signal is input to the optical demodulator, and the signal to be modulated is input to the optical phase modulator.

[0021] The coded signal generator generates a combined coded signal, which is input to an optical phase modulator to modulate the signal to be modulated, thereby generating a modulated laser signal. The modulated laser signal is then output to the optical amplifier.

[0022] The optical amplifier amplifies the modulated laser signal and outputs it to the optical transceiver system. The transceiver system emits the amplified laser signal, which illuminates the target and generates a backscattered signal. The backscattered signal is received by the receiving mirror in the optical transceiver system and extracted as a target echo signal. Both the target echo signal and the local oscillator signal are input to the optical demodulator. The output of the optical demodulator is connected to a photodetector, and the output signal of the photodetector is sampled by an analog-to-digital converter and then input to a signal processor.

[0023] Furthermore, an optical frequency shifter for closed-loop control is provided in front of the phase modulator. The signal processor calculates the target Doppler output and sends it to the optical frequency shifter, thereby controlling the optical frequency shifter to generate a corresponding frequency shift to achieve target motion compensation.

[0024] The advantages of this invention over the prior art are:

[0025] 1. Target Doppler extraction can be achieved simply by adjusting the encoding signal, which can easily and effectively solve the problem of low Doppler tolerance in phase-coded coherent lidar.

[0026] 2. By embedding information, the ability to resist crosstalk between radars is improved, and local information interconnection between radars can be realized at the same time. Attached Figure Description

[0027] Figure 1 This is a flowchart of a coherent lidar ranging, velocimetry, and super-resolution imaging method based on combined coding.

[0028] Figure 2 This is an implementation scheme for combined encoding.

[0029] Figure 3 This is a schematic diagram of a coherent lidar ranging, velocimetry, and super-resolution imaging device based on combined coding.

[0030] Figure 4 This is a schematic diagram of another coherent lidar ranging, velocimetry, and super-resolution imaging device based on combined coding.

[0031] The above figures include the following reference numerals: 1. Laser; 2. Optical phase modulator; 3. Encoded signal generator; 4. Optical amplifier; 5. Optical transceiver system; 6. Optical demodulator; 7. Photodetector; 8. Analog-to-digital converter; 9. Signal processor; 10. Optical frequency shifter. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0033] See appendix Figure 1 As shown, Figure 1 This is a flowchart of a coherent lidar ranging, velocimetry, and super-resolution imaging method based on combined coding, according to an embodiment of the present invention.

[0034] The coherent lidar ranging, velocimetry, and super-resolution imaging method based on combined coding according to embodiments of the present invention includes the following steps:

[0035] S1: Generate a combined code as a driving signal to modulate the laser;

[0036] S2: Output a modulated laser signal, and the modulated laser signal illuminates the target under test and generates backscattered light; extract the echo signal from the backscattered light, use the strongest single-frequency component in the echo signal as the target radial Doppler to complete the velocity measurement, and compensate for the target radial Doppler through signal processing;

[0037] S3: Use a matched filter to obtain target distance information from the echo signal, and at the same time determine the starting point of each combination code in the target distance information data to rearrange the echo signal into a data matrix;

[0038] S4: Based on prior information about the combined coding distribution, the data matrix is ​​divided into different sub-matrices;

[0039] S5: Use the synthetic aperture imaging algorithm to achieve super-resolution imaging on the radar data submatrix in the submatrix, and perform key decoding after carrier recovery on the local information submatrix in the submatrix to obtain information.

[0040] In step S1, the combined coding must include a code pattern with good autocorrelation performance as a radar data segment for matched filtering to achieve target ranging and determine the starting point of the combined coding in the echo signal.

[0041] In step S1, if the length of the radar data segment in the combined encoding is N, then each end of it needs a 0-value interval with a length not shorter than N to ensure the correlation performance when performing matched filtering on the echo signal later.

[0042] In step S1, the 0-value interval must be guaranteed to have a certain proportion in the combined encoding so that the spectral intensity of the single-frequency signal is higher than that of the broadband region, thereby accurately extracting and compensating for the target radial Doppler.

[0043] In step S1, the combined encoding can embed a signal modulated with a specific orthogonal code as the key. Only by decoding with this key can the information be obtained, thus enabling local information interconnection between radars. If a local identification code is embedded in this way, the ability to resist crosstalk between radars can be improved.

[0044] In step S1, the combined encoding can embed more types of data, and the communication protocol can be fixed.

[0045] See appendix Figure 2 As shown, Figure 2 One proposed implementation scheme for combined encoding includes radar data segments, local information segments, and zero-value intervals. The radar data segments in the combined encoding have a length of N, with zero-value intervals at both ends of a length not shorter than N / 2. This ensures that there is no interference from other signals during subsequent matched filtering of the echo signal. The zero-value intervals have a certain proportion in the combined encoding, so that the spectral intensity of the single-frequency signal is higher than that of the broadband region, thereby ensuring accurate extraction and compensation of the target's radial Doppler. The combined encoding can be directly generated by an FPGA or AWG. In another embodiment, the length of the corresponding data segments can be increased or decreased according to the pulse compression ratio or inter-radar communication requirements. To increase signal transmission reliability, CRC checks can be embedded in the combined encoding.

[0046] See appendix Figure 3 As shown, Figure 3 This is a schematic diagram of a coherent lidar ranging, velocimetry, and super-resolution imaging device based on combined coding. The device includes: a laser 1, a coded signal generator 3, an optical phase modulator 2, an optical amplifier 4, an optical transceiver system 5, an optical demodulator 6, a photodetector 7, an analog-to-digital converter 8, a signal processor 9, and an optical frequency shifter 10. The laser 1 outputs two signals: one is a local oscillator signal, and the other is a signal to be modulated. The local oscillator signal is input to the optical demodulator 6, and the signal to be modulated is input to the optical phase modulator 2. The coded signal generator 3 generates a combined coded signal, which is input to the optical phase modulator 2 to modulate the signal to be modulated, thereby generating a modulated laser signal. The modulated laser signal is output to the optical amplifier 4.

[0047] The optical amplifier 4 amplifies the adjusted laser signal and outputs it to the optical transceiver system 5. The optical transceiver system 5 emits the amplified laser signal, which illuminates the target and generates a backscattered signal. The backscattered signal is received by the receiving mirror in the optical transceiver system and extracted as the target echo signal. The target echo signal and the local oscillator signal are both input to the optical demodulator 6. The output of the optical demodulator 6 is connected to the photodetector 7. The output signal of the photodetector 7 is sampled by the analog-to-digital converter 8 and then input to the signal processor 9.

[0048] The optical phase modulator 2 is preceded by an optical frequency shifter 10 for closed-loop control. The signal processor 9 calculates the target Doppler output and sends it to the optical frequency shifter 10, thereby controlling the optical frequency shifter 10 to generate a corresponding frequency shift, thus achieving closed-loop control and realizing target motion compensation in hardware. See Appendix. Figure 4 As shown, Figure 4 This is a schematic diagram of another coherent lidar ranging, velocimetry, and super-resolution imaging device based on combined coding.

[0049] After extracting the target Doppler signal in the signal processor 9, the device needs to convert the received signal to the frequency domain and compensate for the corresponding phase based on the Doppler value and the analog-to-digital converter sampling rate to achieve target motion compensation. Compared to... Figure 3 The device shown omits the optical frequency shifter 10, so target motion compensation needs to be implemented on the signal processor.

[0050] The above examples are one embodiment of the present invention, but not all embodiments. Any changes, combinations, simplifications made without departing from the essential principles of the present invention are included within the protection scope of the present invention.

Claims

1. A ranging, velocimetry, and imaging method based on combined coding, characterized in that, The method includes the following steps: S1: Generate a combined code as a driving signal to modulate the laser; the radar data segment in the combined code has a length of N, and both ends have a 0 value interval with a length not less than N / 2; S2: Output a modulated laser signal, and the modulated laser signal illuminates the target under test and generates backscattered light; extract the echo signal from the backscattered light, use the strongest single-frequency component in the echo signal as the target radial Doppler to complete the velocity measurement, and compensate for the target radial Doppler through signal processing; S3: Use a matched filter to obtain target distance information from the echo signal, and at the same time determine the starting point of each combination code in the target distance information data to rearrange the echo signal into a data matrix; S4: Based on prior information about the combined coding distribution, the data matrix is ​​divided into different sub-matrices; S5: Use the synthetic aperture imaging algorithm to achieve super-resolution imaging on the radar data submatrix in the submatrix, and perform key decoding after carrier recovery on the local information submatrix in the submatrix to obtain information.

2. The ranging, velocimetry, and imaging method based on combined coding as described in claim 1, characterized in that, The radar data segment in the combined encoding has a length of N, and both ends have a 0 value interval with a length not less than N / 2; the radar data sub-matrix is ​​composed of multiple pulses of the radar data segment.

3. The ranging, velocimetry, and imaging method based on combined coding as described in claim 2, characterized in that, The 0-value interval has a certain proportion in the combined coding so that the spectral intensity of the single-frequency signal is higher than that of the broadband region, thereby accurately extracting and compensating for the target radial Doppler.

4. The ranging, velocimetry, and imaging method based on combined coding as described in claim 1, characterized in that, The combined encoding embeds a signal modulated with orthogonal codes as the key. Information is obtained by decoding the key, thereby enabling local information interconnection between radars.

5. The ranging, velocimetry, and imaging method based on combined coding as described in claim 1, characterized in that, The combined encoding embeds the local identification code.

6. A ranging, velocimetry, and imaging device based on combined coding, characterized in that, The device includes: a laser, an encoded signal generator, an optical phase modulator, an optical amplifier, an optical transceiver system, an optical demodulator, a photodetector, an analog-to-digital converter, and a signal processor, wherein... The laser outputs two signals: a local oscillator signal and a signal to be modulated. The local oscillator signal is input to the optical demodulator, and the signal to be modulated is input to the optical phase modulator. The encoding signal generator produces a combined encoding signal, which is then input to the optical phase modulator to modulate the signal to be modulated, generating a modulated laser signal. The modulated laser signal is output to the optical amplifier. The radar data segment in the combined encoding has a length of N, with both ends having a 0 value interval of not less than N / 2. The optical amplifier amplifies the modulated laser signal and outputs it to the optical transceiver system. The transceiver system emits the amplified laser signal, which illuminates the target and generates a backscattered signal. The backscattered signal is received by the receiving mirror in the optical transceiver system and extracted as a target echo signal. Both the target echo signal and the local oscillator signal are input to the optical demodulator. The output of the optical demodulator is connected to a photodetector, and the output signal of the photodetector is sampled by an analog-to-digital converter and then input to a signal processor.

7. The ranging, velocimetry, and imaging device based on combined coding as described in claim 6, characterized in that: An optical frequency shifter for closed-loop control is provided in front of the optical phase modulator. The signal processor calculates the target Doppler output and sends it to the optical frequency shifter, thereby controlling the optical frequency shifter to generate a corresponding frequency shift in order to achieve target motion compensation.

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