An optical processing device for adapting multi-channel forward looking radar signal parallel processing

Abstract

An optical processing device adapted to parallel processing of multi-channel forward-looking radar signals is disclosed. This device preprocesses high-throughput radar signals in the analog domain by moving the highly complex steps in the radar imaging algorithm to the optical domain for instantaneous parallel computation. During the processing, the data volume is downsampled and extracted, which reduces the requirements of imaging on back-end electrical sampling and computation, thereby enabling high real-time radar forward-looking imaging.

Description

Technical Field

[0001] This invention belongs to the field of optical computing technology, specifically an optical processing device adapted for parallel processing of multi-channel forward-looking radar signals. Background Technology

[0002] Multi-channel forward-looking radar, with its large azimuth real aperture, can fundamentally solve the problems of lack of Doppler and left-right blurring in the forward-looking imaging area, enabling the radar to acquire information in all directions. While its advantages are obvious, multi-channel forward-looking radar faces processing bottlenecks due to high data volume and computational demands: the MIMO system, non-scanning, and ultra-wideband characteristics of forward-looking imaging (resolution depends on the physical aperture size and bandwidth, and imaging quality depends on the MIMO scale and bandwidth) result in massive data volumes. Under traditional electronic processing architectures, high processing latency hinders the real-time advantage of multi-channel forward-looking radar; a large amount of digital processing resources are required, with each additional receiving channel necessitating an additional ultra-high-speed ADC and processor; high-frequency signal transmission suffers from high loss and poor stability, requiring a synchronization accuracy of 20 ps between all channels. As radar signals evolve towards millimeter-wave frequencies and ultra-wideband, the processing speed of electronic ADCs and processors will inevitably become insufficient. Research shows that optical computing has significant advantages over electronic architectures in terms of multi-channel parallel processing speed, transmission, bandwidth, and synchronization stability, and has the potential to be adapted to multi-channel forward-looking imaging.

[0003] However, despite some research attempts to apply optical computing techniques to radar systems, these studies still have certain limitations. For example, Salvatore Maresca's team (2020) first introduced photonic systems into MIMO radar, extending the coherence factor of distributed radar. They experimentally demonstrated that a photonic input-output radar system can maximize centralized data fusion, providing unprecedented resolution capabilities. However, the main contribution of this approach lies in improving the RF transmission link of distributed radar, using optical transmission to ensure coherence and resolution, but it does not address the application of optical devices in signal processing, nor does it solve the high-throughput data processing challenges brought about by centralized data fusion. Simin Li's team (2020) proposed a chip-based microwave photonic radar based on a silicon photonics platform. An integrated optical modulator completed the delinear frequency modulation of FMCW, achieving high-precision ranging results with a resolution of 2.7 cm and an error of less than 2.75 mm, and realizing inverse synthetic aperture imaging of multiple complex contour targets. However, this approach is only applicable to FMCW radar systems, and multi-channel acquisition is still necessary, failing to fundamentally solve the bottleneck problem of data processing. Although Bindong Gao's team (2021) simultaneously generated M LFM transmit signals using photo-generated radio frequency technology and decomposed N echo signals into MN intermediate frequency signals using photo-decomposition linear frequency modulation technology, thereby reducing the data sampling rate requirement, this method still requires processing a large amount of sampling channel data and failed to effectively reduce the overall data processing volume of the system.

[0004] In summary, although optical computing technology has achieved some initial results in the application of multi-channel forward-looking radar, existing solutions still have many limitations, especially in the application of optical devices in signal processing and how to solve the problem of high-throughput data processing, which still need further in-depth research and exploration. Summary of the Invention

[0005] This invention addresses the shortcomings of existing electrical architecture technologies in processing high-throughput radar signals by proposing an optical processing device adapted for parallel processing of multi-channel forward-looking radar signals. The aim is to solve the processing bottleneck of high-throughput echo signals in multi-channel forward-looking radar systems. This device migrates the highly complex steps of the radar imaging algorithm to the optical domain for instantaneous parallel computation, while simultaneously compressing the data volume during processing. This reduces the requirements for back-end electrical sampling and computation, achieving high real-time radar forward-looking imaging. The device preprocesses the high-throughput radar signal in the analog domain: it moves the highly complex steps of the radar imaging algorithm to the optical domain for instantaneous parallel computation, and compresses the data volume during processing, retaining only the imaging time-domain data required for subsequent electrical domain processing. This reduces the requirements for back-end electrical sampling and computation, enabling high real-time radar forward-looking imaging.

[0006] The technical solution of the present invention is as follows:

[0007] An optical processing device adapted for parallel processing of multi-channel forward-looking radar signals is disclosed for parallel processing of N×M (M transmit, N receive) MIMO radar echo data. Its features include: M radar transmit elements, N radar receive elements, N down-conversion components, N light sources and modulators of different wavelengths, two N-channel wavelength division multiplexers, two optical delay arrays containing N independent branches, one N-channel wavelength demultiplexer, two one-dimensional optical convolution devices with orders T0×f and Q respectively, two optical switching devices, and a back-end electrical processor for a photodetector.

[0008] The receiving front end consists of N radar receiving array elements and N down-conversion components, and the output N baseband signals are connected to the corresponding modulation units.

[0009] The light source array consists of N light sources of different wavelengths, which are connected to the local oscillator input of the optical modulation array;

[0010] The multi-channel optical modulation array consists of N modulators. The radio frequency terminal of each modulator is connected to the baseband output port of the receiving front end with the corresponding number, and the local oscillator terminal is connected to the light source unit with the corresponding number. Different numbered light sources have different wavelengths and are used to modulate the broadband echo signal into the optical domain for processing. The modulation output is connected to the optical delay array.

[0011] The first optical delay array consists of N independent adjustable optical delay devices. The input of each delay device is connected to the output of the corresponding numbered optical modulator. All N delay devices have digital circuit control interfaces, and the delay amount can be set by a program. The delay output is connected to a wavelength division multiplexer.

[0012] A wavelength division multiplexer is used to combine N optical modulation signals of different wavelengths together to achieve wavelength multiplexing. The single output after multiplexing is connected to an optical computing device array.

[0013] The first optical convolution kernel is composed of a T0×f tapped FIR filter, which can simultaneously perform convolution operations on N input wavelength signals to achieve pulse compression of radar signals. The output is connected to optical switch one.

[0014] The first optical switch has one input and one output. The input is the output of the optical computing device and has a digital circuit control interface. The signal can be turned on and off by program control. Its output is connected to the second optical computing device.

[0015] The second optical convolution kernel consists of a Q-tap ​​FIR filter, which performs convolution calculations on N input wavelength signals with fixed coefficients simultaneously to achieve pre-aliasing of analog signals, and the output is connected to optical switch two.

[0016] The second optical switch has one input and one output. The input is connected to the output of the optical computing device and has a digital circuit control interface. The signal can be controlled to be turned on and off by a program. Its output is connected to the wave decomposition and multiplexing module.

[0017] The wavelength demultiplexing module separates a single channel of N optical modulation signals of different wavelengths into N independent branches. The output of the wavelength demultiplexer is connected to an optical delay array.

[0018] The second optical delay array consists of N independent fixed optical delay devices. The input of each delay device is connected to the output of the corresponding numbered wave demultiplexing module, and the delay output is connected to the optical combiner.

[0019] An optical combiner combines N delayed optical signals of different wavelengths to form time-division multiplexed frame signals corresponding to different receiving channels, which are then output to a photoelectric detection device.

[0020] The photoelectric detection device consists of a broadband photodetector, which is used to convert the processed optical signal into an electrical signal and then transmit it to the back-end electrical processor.

[0021] The back-end electrical processor array consists of a high-speed ADC module and an electrical processor. The ADC samples and quantizes the optically processed signal, separates each frame, and stores them in different memory units via DMA. The processor first performs an FFT on the frame signal to obtain the image spatial spectrum sample values, then fills the sample values ​​into an empty two-dimensional array according to the pre-calculated spatial spectrum position coordinates, and finally performs a two-dimensional IFFT on the array to obtain the radar forward-looking image.

[0022] Preferably, the wavelength spacing of each light source in the light source array meets the multiplexing bandwidth requirements of the wavelength division multiplexer, and the wavelength uniqueness is achieved through digital tuning control.

[0023] Preferably, the first optical convolution kernel and the second optical convolution kernel are used to realize pulse compression of radar signals and pre-aliasing of analog signals, respectively. The number of taps T0×f of the first optical convolution kernel is determined by the pulse width and bandwidth of the radar transmitted signal and is used to complete matched filtering in the optical domain. The number of taps Q of the second optical convolution kernel is equal to the data decimation factor and is used to complete time-domain pre-aliasing in the optical domain, reducing the amount of data in a single channel by a factor of Q.

[0024] Preferably, the first optical delay array and the second optical delay array are used to perform phase compensation and time-domain delay on the optical modulation signal, respectively, and the first optical delay array has an adjustable delay amount, while the second optical delay array has a fixed delay amount.

[0025] Preferably, the wavelength division multiplexer and the wavelength demultiplexing module are used to realize wavelength multiplexing and separation of optical signals, and the wavelength division multiplexer combines N optical signals of different wavelengths into a single signal, while the wavelength demultiplexing module separates the single signal into N optical signals of different wavelengths.

[0026] Preferably, the time-division multiplexed frame signal output by the optical combiner achieves non-overlapping combining of multi-channel signals through a fixed delay of I×T1 / Q (I=0,1,…,N-1).

[0027] The technical advantages of this invention are:

[0028] (1) It has ultra-wideband, high-throughput radar signal processing capabilities. The bandwidth is determined by the optical modulator and is not limited by the sampling rate of the back-end electronic ADC, which is of great significance to improving radar imaging resolution.

[0029] (2) It can complete the frequency domain extraction stage in the imaging algorithm in the optical simulation domain, reducing the total amount of back-end data of a single imaging to hundreds of times that of the traditional scheme, while ensuring that the imaging accuracy is not inferior to that of the traditional scheme.

[0030] (3) It can process multi-channel echo signals in parallel, giving full play to the architectural advantages of MIMO radar's "fast-shot" imaging, and avoiding the disadvantages of traditional multi-channel acquisition and single-channel time-division acquisition schemes, such as high computational complexity, poor real-time performance, and high equipment cost. Attached Figure Description

[0031] Figure 1 A schematic diagram of an embodiment of an optical processing device for parallel processing of multi-channel forward-looking radar signals according to the present invention, where N=8 and M=3;

[0032] Figure 2 It demonstrates the transformation of signal waveforms during multi-channel parallel data processing and time-domain decimation.

[0033] Figure 3 This is a schematic diagram of the process from sampling signal to image in the back-end electronic processor. Detailed Implementation

[0034] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, providing detailed implementation methods and structures. However, the scope of protection of the present invention is not limited to the following embodiments. The terms "left" and "right" used below refer to the placement positions shown in the figures, not to the actual system positions. The actual system should maintain the same connection order as the figures.

[0035] An optical processing device adapted for parallel processing of multi-channel forward-looking radar signals is disclosed. This device processes multi-channel forward-looking radar signals composed of M transmitting units and N receiving units. The transmitted signal length is T0, the acquired signal window length is T1, the data rate reduction factor is Q, and the back-end ADC sampling rate is F. The device's structure and function are as follows:

[0036] The receiving front-end 112 consists of N independent receiving antenna feeders and down-conversion components, used to receive radar echo signals and down-convert them to baseband signals; the baseband signal output by each receiving front-end is connected to the corresponding modulation unit.

[0037] The light source array consists of N light sources of different wavelengths, used to generate a sequence of light carrying signals. Each light source is connected to the local oscillator input of the corresponding modulator in the optical modulation array.

[0038] An optical modulation array consists of N modulators, each with its radio frequency (RF) terminal connected to the corresponding numbered baseband output port of the receiver front end. The modulators modulate the baseband signal into the optical domain for processing.

[0039] The first optical delay array consists of N independent adjustable optical delay units, used for phase compensation of optical modulation signals. Each delay unit has a digital circuit control interface, and the delay amount can be set by program.

[0040] A wavelength division multiplexer combines N optical modulation signals of different wavelengths to achieve wavelength multiplexing. The single output of the multiplexed signal is then connected to an optical computing device array.

[0041] Optical computing device array (including a first optical convolution kernel, a first optical switch, a second optical convolution kernel, and a second optical switch):

[0042] The first optical convolution kernel consists of a T0×f tapped FIR filter, which is used to perform convolution operations on the input N wavelength signals to achieve pulse compression of radar signals.

[0043] The first optical switch, used to control the on / off state of the signal, is connected between the first optical convolution kernel and the second optical convolution kernel;

[0044] The second optical convolution kernel consists of a Q-tap ​​FIR filter that performs convolution calculations on N input wavelength signals simultaneously with fixed coefficients to achieve pre-aliasing of analog signals.

[0045] The second optical switch, used to control the on / off state of the signal, is connected between the second optical convolution kernel and the wavelet decomposition and multiplexing module;

[0046] Wavelength demultiplexing module separates a single channel of N optical modulation signals of different wavelengths into N independent branches.

[0047] The second optical delay array consists of N independent fixed optical delay devices, which are used to further delay the separated optical signals.

[0048] An optical combiner combines N delayed, time-division multiplexed optical signals of different wavelengths to form time-division multiplexed frame signals corresponding to different receiving channels.

[0049] The photoelectric detection device consists of a broadband photodetector, which is used to convert the processed optical signal into an electrical signal and transmit it to the back-end electrical processor.

[0050] The back-end electrical processor array consists of a high-speed ADC module and an electrical processor. The ADC samples and quantizes the optically processed signal and stores each frame separately. The processor performs FFT and two-dimensional IFFT processing on the frame signals to obtain the radar forward-looking image.

[0051] Workflow:

[0052] The radar transmits a signal to illuminate the target, and the echoes from N receiving units (numbered I = 0, 1, ..., N-1) are down-converted to baseband output. N independent light sources generate optical signals of different wavelengths, which are mixed with N baseband signals by N modulators, modulating the signals into the optical domain for processing. The N optical modulation signals undergo phase compensation through N independent delay devices in a delay array. After phase compensation, the N optical modulation signals are combined into a single multiplexed signal output by an N-channel wavelength division multiplexer. The multiplexed signal undergoes pulse compression using a first optical convolution kernel of length T0×f. After convolution, a first optical switch applies a rectangular window of time width T1 to the output signal. The signal, after range gate filtering, undergoes time-domain pre-aliasing and decimation using a second convolution kernel of length Q. After convolution, a second optical switch applies a rectangular window of time width T1 / Q to the output signal. After windowing, the optical signal is re-separated into N independent optical signals of different wavelengths by an N-channel wavelength division multiplexer. The delay is set to I×T1 / Q according to the number of each signal. After the delay, the N signals are combined by an N-channel wavelength division multiplexer, and finally converted to the electrical domain by a photodetector for final imaging.

[0053] This embodiment of the device achieves parallel processing of N-channel signals. By decimation, the data volume per channel is reduced by a factor of Q. Delayed combining reduces the multi-channel signal to a single-channel signal, reducing the required number of sampling channels for the electronic ADC to 1, while maintaining the same sampling rate. Assuming the imaging resolution is set to n×n, after optical domain front-end processing, the computational load per frame for the back-end electronic processor is reduced to... times.

[0054] Please see Figure 1When N=8, M=3, T0=3.2ns, T1=150ns, Q=15, F=20GHz, and n=100, this embodiment includes 3 radar transmitting elements, 8 radar receiving elements, 8 down-conversion components, 8 light sources and modulators of different wavelengths, 2 8-channel wavelength division multiplexers, 2 optical delay arrays containing 8 independent branches, 1 8-channel wavelength demultiplexer, 2 one-dimensional optical convolution devices with orders T0×f and Q respectively, and 2 optical switching devices. The specific connection methods and functional descriptions of each device are as follows:

[0055] In this embodiment, the signal is output time-division multiplexed by three transmitting arrays 110 to illuminate the forward-looking target. The echo is fed into an antenna system composed of eight receiving array elements 111, and each element undergoes independent down-conversion at the receiving front-end 112 to obtain the corresponding baseband signal. A light source array 113 generates a light sequence carrying the signal; each light source 113 outputs a different wavelength, which in this embodiment are eight different wavelengths. The optical power generated by the light sources 113 is replicated into eight parts at a 1:8 ratio using a beam splitter, and each part is connected to the optical input port of one of the eight modulators 114. The RF signal input port of the modulator is connected to the down-converted baseband signal, and the output port of the modulator 114 is connected to a delay array 115. The delay array aligns the echo envelope, with the delay being the negative propagation delay of the distance from the receiving element to the origin. The output of the delay array is connected to the input port of a wavelength division multiplexer array 116. The output port of the wavelength division multiplexer 116 is connected to an optical convolution kernel 117, wherein the convolution kernel has 64 levels. The output of the optical convolution is connected to optical switch 118, and a time-domain window of T1 = 150 ns is applied to the output signal. The windowed output is then connected to optical convolution kernel 119, with a kernel level of 15. The output of the convolution kernel is connected to optical switch 120, and a time-domain window of T2 = 10 ns is applied to the output signal. The output of the optical switch is connected to an 8-channel wavelength division multiplexer 121. The optical signal is re-separated into 8 independent optical signals of different wavelengths by the 8-channel wavelength division multiplexer. These signals are connected to a delay array 122, with a delay of I × 10 ns (I = 0, 1, 2, 3, 4, 5, 6, 7) set according to the number of each signal. After delay, the signals do not overlap in the time domain. The 8 signals are then combined by an 8-channel wavelength division multiplexer 123, and finally converted to the electrical domain by a photodetector 124. The back-end processor 125 samples and digitizes the signal using a 20GHz ADC. Each frame is separated into 10ns frames and stored in eight different memory units via DMA. The processor first performs an FFT on the eight frames to obtain the image spatial spectrum sample values. Then, based on pre-calculated spatial spectrum position coordinates, the sample values ​​are filled into an empty 100×100 two-dimensional array. After all frames are filled, a two-dimensional IFFT is performed on the array to obtain the radar forward-looking image.

[0056] This embodiment of the device enables parallel processing of 8 signals. By decimation, the data volume of a single channel is reduced by 15 times. By delaying and combining, the multi-channel signal is reduced to a single signal. The number of sampling channels required by the electronic ADC is reduced to 1, and the sampling rate is 20G. After optical domain front-end processing, the number of multiplications required by the back-end electronic processor per frame is reduced by 794,970, and the imaging time is reduced by 23 times.

[0057] Figure 2 The signal transformation process for time-domain decimation in an optical processing device is given when N=8, M=3, T0=3.2ns, T1=150ns, Q=15, F=20GHz, and n=100. Figure 3 This is a schematic diagram of the process from sampled signal to image in the back-end electrical processor. As shown in the figure, the operations performed by the back-end electrical processor include: storing the signal sampled by the ADC in frames; performing FFT on each frame of signal to generate spatial spectrum sample values; filling the sample values ​​into a preset two-dimensional array; and generating a radar forward-looking image through two-dimensional IFFT.

Claims

1. An optical processing device for adapting parallel processing of multi-channel forward looking radar signals, for parallel processing of NxM MIMO radar echo data, characterized in that, include: The receiving front end consists of N radar receiving array elements and N down-conversion components, used to receive radar echo signals and down-convert them to baseband signals. The output N baseband signals are respectively connected to the corresponding optical modulation arrays. The light source array consists of N light sources with different wavelengths, each of which is connected to the local oscillator input of the optical modulation array. An optical modulation array consists of N modulators. The radio frequency terminal of each modulator is connected to the baseband output port of the corresponding receiving front end, and the local oscillator input terminal is connected to the output terminal of the corresponding light source, which is used to modulate the baseband signal into the optical domain. The first optical delay array consists of N adjustable optical delay units. The input of each adjustable optical delay unit is connected to the output of the modulator, which is used to perform phase compensation on the optical modulation signal and has a digital circuit control interface to set the delay amount. A wavelength division multiplexer is used to combine N optical modulation signals of different wavelengths into a single multiplexed signal. The first optical convolution kernel, consisting of a T0×f tapped FIR filter, performs pulse compression on the multiplexed optical signal; The first optical switch, used to control the on / off state of the signal, is connected between the first optical convolution kernel and the second optical convolution kernel; The second optical convolution kernel, composed of a Q-tap ​​FIR filter, pre-aliased and decimated the signal after it has been controlled by the first optical switch, reducing the amount of data per channel by a factor of Q. The wavelength decomposition and multiplexing module separates the processed single-channel N different wavelength optical modulation signals into N independent branches; The second optical delay array consists of N independent fixed optical delay units, which are used to adjust the time delay of the separated signals; An optical combiner combines N delayed optical signals of different wavelengths into a time-division multiplexed frame signal. The photoelectric detection device is used to convert the combined optical signal into an electrical signal and transmit it to the back-end electrical processor array, and obtain the radar forward-looking image through the imaging algorithm.

2. The optical processing device for parallel processing of multi-channel forward-looking radar signals according to claim 1, characterized in that, The wavelength spacing of each light source in the light source array meets the multiplexing bandwidth requirements of the wavelength division multiplexer, and the uniqueness of the wavelength is achieved through digital tuning control.

3. The optical processing device for parallel processing of multi-channel forward-looking radar signals according to claim 1, characterized in that, The first optical convolution kernel and the second optical convolution kernel are used to realize the pulse compression of radar signals and the pre-aliasing of analog signals, respectively. The number of taps T0×f of the first optical convolution kernel is determined by the pulse width and resolution requirements of the radar transmitted signal and is used to complete matched filtering in the optical domain. The number of taps Q of the second optical convolution kernel is equal to the data decimation factor and is used to complete time-domain pre-aliasing in the optical domain, reducing the amount of data in a single channel by a factor of Q.

4. The optical processing device for parallel processing of multi-channel forward-looking radar signals according to claim 1, characterized in that, The first optical delay array and the second optical delay array are used to perform phase compensation and time-domain delay on the optical modulation signal, respectively. The first optical delay array has an adjustable delay amount, and the second optical delay array has a fixed delay amount.

5. The optical processing device for parallel processing of multi-channel forward-looking radar signals according to claim 1, characterized in that, The wavelength division multiplexer and wavelength demultiplexing module are used to realize wavelength multiplexing and separation of optical signals. The wavelength division multiplexer combines N optical signals of different wavelengths into a single signal, and the wavelength demultiplexing module separates the single signal into N optical signals of different wavelengths.

6. The optical processing device for parallel processing of multi-channel forward-looking radar signals according to claim 1, characterized in that, The time-division multiplexed frame signal output by the optical combiner achieves non-overlapping combining of multi-channel signals through a fixed delay of I×T1 / Q, where I=0,1,…,N-1.

7. An optical processing device for parallel processing of multi-channel forward-looking radar signals according to claim 1, characterized in that, The operations performed by the back-end electrical processor include: - Store the ADC-sampled signal in frames; - Perform FFT on each frame of signal to generate spatial spectrum sample values; - Fill the sampled values ​​into a preset two-dimensional array; - Generate radar forward-looking imaging map using 2D IFFT.

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