Wideband radio frequency transmitting channel amplitude and phase fluctuation correction system based on photonic deskewing reception
By using photon deslant receiving technology to convert radio frequency signals into low-intermediate frequency signals for digital acquisition, the problem of amplitude and phase fluctuation correction in broadband radio frequency transmission channels is solved, achieving efficient amplitude and phase correction and improving imaging quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA ELECTRONIC TECH GRP CORP NO 38 RES INST
- Filing Date
- 2023-11-30
- Publication Date
- 2026-07-28
AI Technical Summary
Existing technologies struggle to effectively correct amplitude and phase fluctuations in broadband radio frequency transmission channels. In particular, in ultra-wideband imaging radar systems, digital acquisition technology struggles to achieve direct digital acquisition of radio frequency signals with bandwidths of several GHz, leading to a decline in imaging quality.
A broadband RF transmission channel amplitude and phase fluctuation correction system based on photonic deskewing reception is adopted. The broadband RF broadband LFM signal is converted into a low intermediate frequency signal for digital acquisition through a broadband photonic deskewing reception link. The amplitude and phase fluctuation information in the broadband RF LFM signal is demodulated by a digital demodulation parameter extraction unit to generate channel amplitude and phase correction parameters, thereby realizing digital predistortion amplitude and phase fluctuation correction.
This reduces the performance requirements of the digital acquisition ADC, enables amplitude and phase fluctuation correction of the broadband radio frequency transmission channel, and improves imaging quality.
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Figure CN117420519B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microwave photonic radar technology and relates to a broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photonic deskewing reception. Background Technology
[0002] The range resolution of the imaging radar is:
[0003]
[0004] Where c is the speed of light and B is the bandwidth of the imaging radar pulse.
[0005] To achieve higher precision imaging, imaging radar systems are increasingly expanding their instantaneous operating bandwidth. In the millimeter-wave and terahertz frequency bands, the operating bandwidth of imaging radar can reach several GHz or even tens of GHz (10). 9 hertz).
[0006] However, it is not only the bandwidth of the imaging radar system that affects image quality; amplitude and phase nonlinear fluctuations in the radar system's radio frequency channel can also lead to a decrease in image quality. As shown in Figures 6(a) and 6(b), a one-dimensional range pulse compression imaging simulation was performed using an LFM (Linear Frequency Modulation) signal. Figure 6(a) shows the pulse compression result of an ideal LFM signal, while Figure 6(b) shows the pulse compression result of a distorted LFM signal affected by channel amplitude and phase nonlinear fluctuations. Channel amplitude and phase nonlinear fluctuations cause amplitude and phase distortion of the LFM signal, resulting in problems such as main lobe broadening, sidelobe elevation, and stray echoes in the pulse-compressed one-dimensional range image.
[0007] To achieve better imaging results, it is necessary to correct the in-band amplitude and phase fluctuations of the radio frequency channel. In the imaging radar system with analog deskewing reception, ultra-wideband signals can be generated by frequency doubling, but existing digital technologies are difficult to directly digitize and correct the amplitude and phase fluctuations of radio frequency signals with bandwidths of several GHz or more.
[0008] High-end oscilloscopes can achieve sampling rates of up to 100 Gsps (10 9 While sampling rates can exceed 50 GHz per second and analog bandwidths can reach over 50 GHz, this still falls short of the direct digital acquisition requirements for broadband radio frequency signals in imaging applications (such as millimeter-wave automotive radar and terahertz imaging applications). Furthermore, using instruments for in-band amplitude and phase ripple correction is costly and difficult to apply for frequent calibrations in imaging radar applications. Therefore, amplitude and phase ripple correction methods for broadband radio frequency transmission channels have become a challenge in improving radar imaging quality.
[0009] In existing technologies, amplitude and phase correction of RF channels is mainly achieved through broadband digital acquisition to digitally correct channel amplitude and phase fluctuations. Taking channel amplitude and phase fluctuation correction based on the least squares method as an example, the main implementation process is as follows: 1) Injecting an ideal LFM signal into the digital transmission channel to obtain a distorted LFM signal with channel amplitude and phase fluctuations; 2) Using a broadband digital acquisition board to digitally acquire the distorted LFM signal to obtain a digitized LFM signal; dividing the spectrum of the ideal LFM signal by the digitized distorted LFM signal in the frequency domain to obtain the frequency response of the transmission channel; 3) Constructing a frequency factor matrix and fitting it using the frequency domain least squares method to obtain the FIR filter coefficients used for channel amplitude and phase equalization; 4) Using an amplitude and phase equalization FIR filter to pre-distort the transmitted LFM signal to obtain the amplitude and phase corrected LFM signal output.
[0010] Since radio frequency transceiver systems are mostly based on digital technology for signal generation and acquisition, the method of correcting in-band amplitude and phase fluctuations through broadband digital acquisition and digital predistortion techniques has high versatility. However, in ultra-wideband imaging radar systems, digital acquisition technology is difficult to achieve direct digital acquisition of radio frequency signals with bandwidths of several GHz. In addition, similar correction techniques include frequency modulation nonlinearity correction methods for linear frequency modulated light sources through coherent detection and active feedback, such as the literature "A Review of Nonlinear Correction of Frequency Modulated Continuous Wave LiDAR Measurement Technology" (Li Chaolin et al., Optoelectronic Engineering, Vol 49, No. 7, 2022). However, the frequency modulation nonlinearity of the light source in this literature is mainly detected by self-heterodyne detection of the frequency nonlinearity of the optical signal, and the instantaneous frequency adjustment of the output optical signal is achieved by directly controlling the light source. Summary of the Invention
[0011] The technical problem to be solved by this invention is how to correct the amplitude and phase fluctuations of a broadband radio frequency transmission channel.
[0012] The present invention solves the above-mentioned technical problems through the following technical solutions: A broadband radio frequency (RF) transmission channel amplitude and phase fluctuation correction system based on photon deskewing receiver includes: a broadband RF transmission channel (1), a broadband photon deskewing receiver link (2), and a digital demodulation parameter extraction unit (3); the input end of the broadband RF transmission channel (1) is connected to the output end of the digital demodulation parameter extraction unit (3), the output end of the broadband RF transmission channel (1) is connected to the input end of the broadband photon deskewing receiver link (2), and the output end of the broadband photon deskewing receiver link (2) is connected to the input end of the digital demodulation parameter extraction unit (3); the broadband RF transmission channel (1) generates a broadband RF LFM signal, the broadband photon deskewing receiver link (2) converts the broadband RF LFM signal into a low-intermediate frequency point frequency signal for digital acquisition, the digital demodulation parameter extraction unit (3) demodulates the transmission channel amplitude and phase fluctuation information carried in the broadband RF LFM signal, generates channel amplitude and phase correction parameters, and realizes broadband RF transmission channel amplitude and phase fluctuation correction in a digital predistortion manner.
[0013] Furthermore, the broadband radio frequency transmission channel includes a digital-to-analog converter (10), a first filter (11), a mixer (12), a second filter (13), a first amplifier (14), a frequency multiplier (15), a third filter (16), and a second amplifier (17) connected in sequence; the input terminal of the digital-to-analog converter (10) is connected to the output terminal of the digital demodulation parameter extraction unit (3) as the input terminal of the broadband radio frequency transmission channel (1), and the output terminal of the second amplifier (17) is connected to the input terminal of the broadband photon de-skewing receiving link (2) as the output terminal of the broadband radio frequency transmission channel (1).
[0014] Further, the broadband photonic de-skewing receiver link (2) includes: a laser (20), an electro-optic modulator (21), an optical filter (22), a first optical power divider (23), a delay fiber (24), a frequency shifting unit (25), a second optical power divider (26), and a detector (27); the laser (20), electro-optic modulator (21), optical filter (22), and first optical power divider (23) are connected in sequence, and one input terminal of the electro-optic modulator (21) serves as the input terminal of the broadband photonic de-skewing receiver link (2) and is connected to the output of the second amplifier (17). The first optical power divider (23) is connected to the input of the delay fiber (24) and the input of the frequency shifting unit (25). The output of the delay fiber (24) is connected to the input of the second optical power divider (26). The output of the frequency shifting unit (25) is connected to the input of the second optical power divider (26). The output of the second optical power divider (26) is connected to the input of the detector (27). The output of the detector (27) is connected to the input of the digital demodulation parameter extraction unit (3) as the output of the broadband photon descrambling receiving link (2).
[0015] Furthermore, the digital demodulation parameter extraction unit (3) includes an analog-to-digital converter (30), a digital demodulator (31), and an amplitude-phase fluctuation parameter extractor (32) connected in sequence; the input end of the analog-to-digital converter (30) is connected to the output end of the detector (27) as the input end of the digital demodulation parameter extraction unit (3), and the output end of the amplitude-phase fluctuation parameter extractor (32) is connected to the input end of the digital-to-analog converter (10) as the output end of the digital demodulation parameter extraction unit (3).
[0016] Further, the system's workflow is as follows: The digital-to-analog converter (10) generates a baseband LFM signal. The baseband LFM signal passes through the first filter (11) and then through the mixer (12) to be converted to an intermediate frequency. The intermediate frequency signal is filtered by the second filter (13) and then amplified by the first amplifier (14). After amplification, it is multiplied by the frequency multiplier (15) to the radio frequency operating frequency band. At this time, the bandwidth of the LFM signal is also expanded by multiples. Finally, the broadband LFM signal is filtered and amplified by the third filter (16) and the second amplifier (17) and then output to the electro-optic modulator (21). The optical carrier output by the laser (20) is injected into the electro-optic modulator (21). The electro-optic modulator (21) modulates the radio frequency broadband LFM signal output by the broadband radio frequency transmission channel (1) into an optical carrier LFM signal. The bias voltage input is controlled to set the electro-optic modulator (21) to work at the zero bias point. At this time, the optical signal output by the electro-optic modulator (21) is a double-sideband carrier suppression signal. The double-sideband carrier suppression signal output by the modulator (21) is filtered out by the optical filter (22) to remove one sideband. The remaining single-sideband carrier suppression signal is split into two paths by the first optical power divider (23). The upper optical LFM signal is introduced into the transmission delay difference with the lower optical path through the delay fiber (24). The lower optical LFM signal is frequency-shifted by the frequency shifting unit (25). The upper and lower optical signals are coherently combined by the second optical power divider (26). The output optical signal is injected into the detector (27) for photoelectric conversion. The analog-to-digital converter (30) collects the electrical signal after photoelectric conversion. After the signal is demodulated by the digital demodulator (31), the LFM signal containing the channel amplitude and phase fluctuation parameters can be obtained. Then, the amplitude and phase fluctuation parameter extractor (32) performs orthogonal down-conversion processing in the digital domain to extract the amplitude and phase fluctuation parameters carried by the distorted LFM signal, thereby generating digital predistortion channel correction parameters, which are sent to the broadband radio frequency transmission channel for transmission predistortion.
[0017] Furthermore, the method for extracting the amplitude and phase fluctuation parameters carried by the distorted LFM signal is as follows: Let the local oscillator frequency of the quadrature downconversion be... The digitally demodulated signal is then:
[0018] The above formula represents the digital zero-IF signal obtained after the ideal linear frequency modulated signal is corrected by the photon de-skewing receiver channel correction system; Let the amplitude and phase characteristics of the ideal system be:
[0019] The amplitude-phase distortion of a real system can be decomposed into the sum of infinitely many simple harmonic distortions. The amplitude-phase characteristics of the system including distortion are expressed as follows:
[0020] Its amplitude-frequency response revolves around a constant value It oscillates in a cosine manner, with phase frequency characteristics revolving around It oscillates in a sinusoidal manner; and These represent the amplitude and frequency of the amplitude-frequency response fluctuations, respectively. and These represent the amplitude and frequency of the phase frequency response fluctuations, respectively. When an LFM signal passes through a distorted system, if the amplitude and phase distortion are slowly varying functions of frequency, then the output signal is equivalent to the product of the frequency domain distortion and the LFM signal, i.e.:
[0021] When the input linear frequency modulated signal contains system amplitude and phase distortion:
[0022] The amplitude fluctuation and phase fluctuation parameters are expressed as follows:
[0023]
[0024] The distorted LFM signal is injected into the photon de-chirping receiver channel correction system, and the complex intermediate frequency signal after digital demodulation is:
[0025] When the time difference When the signal amplitude is very small, if we approximate the first-order Bessel term in the signal amplitude with a small-signal approximation, then the amplitude term of the complex IQ signal is:
[0026] The above formula includes the system's amplitude-frequency response. ; The phase term of the complex IQ signal is:
[0027] in, The linear term, after being removed by linear fitting, leaves the following nonlinear term:
[0028] The above equation gives the instantaneous phase change caused by phase frequency fluctuations, which is the instantaneous frequency drift compared to an ideal linear frequency modulated signal. Accumulating and integrating the remaining nonlinear phase terms yields the nonlinear phase error of the linear frequency modulated pulse. That is, the phase frequency response of the system. .
[0029] Furthermore, the frequency shifting unit (25) includes: an acousto-optic frequency shifter (251) and a microwave source (252); the output end of the first optical power divider (23) is connected to the first input end of the acousto-optic frequency shifter (251), and the output end of the delay fiber (24) is connected to the input end of the second optical power divider (26); the second input end of the acousto-optic frequency shifter (251) is connected to the microwave source (252), and the output end of the acousto-optic frequency shifter (251) is connected to the input end of the second optical power divider (26).
[0030] Further, the frequency shifting unit (25) includes: a microwave source (252), a dual parallel modulator (253), a phase shifter (254), and a third power divider (255); the output terminal of the first optical power divider (23) is connected to the first input terminal of the dual parallel modulator (253), the output terminal of the microwave source (252) is connected to the input terminal of the third power divider (255), the output terminal of the third power divider (255) is connected to the input terminal of the phase shifter (254) and the second input terminal of the dual parallel modulator (253), the output terminal of the phase shifter (254) is connected to the third input terminal of the dual parallel modulator (253), and the output terminal of the dual parallel modulator (253) is connected to the input terminal of the second optical power divider (26).
[0031] Furthermore, the detector (27) is a single photodetector or a balanced photodetector.
[0032] Furthermore, the delay fiber (24) is replaced by an adjustable fiber delay line.
[0033] The advantages of this invention are: This invention uses a broadband radio frequency (RF) transmission channel to generate a broadband RF LFM signal. A broadband photonic de-skewing receiving link converts the RF broadband LFM signal into a low-IF point frequency signal for digital acquisition, reducing the ADC sampling rate requirement for digital amplitude and phase correction. A digital demodulation parameter extraction unit demodulates the transmission channel amplitude and phase fluctuation information carried in the RF broadband LFM signal to generate channel amplitude and phase correction parameters. Broadband RF transmission channel amplitude and phase fluctuation correction is achieved using digital predistortion. This invention uses photonic de-skewing reception to convert the broadband LFM signal into a low-IF signal for digital acquisition, which lowers the performance requirements of the digital acquisition ADC. By splitting the optical LFM signal into two paths and introducing a small transmission delay difference for coherent beat frequency, the channel amplitude and phase fluctuation information carried on the LFM signal can be digitally demodulated from the beat frequency signal, thereby achieving amplitude and phase fluctuation correction of the broadband transmission channel. Attached Figure Description
[0034] Figure 1 This is a structural block diagram of the broadband radio frequency transmission channel amplitude and phase fluctuation correction system for photon deskewing receiving link based on acousto-optic frequency shifter according to Embodiment 1 of the present invention; Figure 2 This is a structural block diagram of the broadband radio frequency transmission channel amplitude and phase fluctuation correction system for photon deskewing receiving link based on acousto-optic frequency shifter according to Embodiment 2 of the present invention; Figure 3 This is a structural block diagram of the broadband RF transmit channel amplitude and phase fluctuation correction system based on dual parallel modulator frequency shifting photon de-skewing receiver link according to Embodiment 3 of the present invention; Figure 4 This is a structural block diagram of the broadband RF transmit channel amplitude and phase fluctuation correction system based on dual parallel modulator frequency shifting photon de-skewing receiver link according to Embodiment 4 of the present invention; Figure 5(a) shows the amplitude and phase nonlinear fluctuation parameters set in the simulation experiment of this invention; Figure 5(b) shows the amplitude and phase error information demodulated in the simulation experiment of this invention; Figure 6(a) shows a one-dimensional range pulse compression imaging of an ideal LFM signal; Figure 6(b) is a one-dimensional distance pulse compression image of the distorted LFM signal. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments: Example 1 like Figure 1 The diagram shows the structural block diagram of the broadband RF transmission channel amplitude and phase fluctuation correction system based on the photon de-skewing receiver link of the acousto-optic frequency shifter in this embodiment of the present invention. It includes: a broadband RF transmission channel (1), a broadband photon de-skewing receiver link (2), and a digital demodulation parameter extraction unit (3). The input end of the broadband RF transmission channel (1) is connected to the output end of the digital demodulation parameter extraction unit (3), the output end of the broadband RF transmission channel (1) is connected to the input end of the broadband photon de-skewing receiver link (2), and the output end of the broadband photon de-skewing receiver link (2) is connected to the input end of the digital demodulation parameter extraction unit (3).
[0037] The broadband radio frequency transmission channel (1) is used to convert the baseband LFM signal into a broadband radio frequency LFM signal. The broadband radio frequency transmission channel includes a digital-to-analog converter (10), a first filter (11), a mixer (12), a second filter (13), a first amplifier (14), a frequency multiplier (15), a third filter (16), and a second amplifier (17) connected in sequence. The input terminal of the digital-to-analog converter (10) is connected to the output terminal of the digital demodulation parameter extraction unit (3) as the input terminal of the broadband radio frequency transmission channel (1), and the output terminal of the second amplifier (17) is connected to the input terminal of the broadband photon de-skewing receiving link (2) as the output terminal of the broadband radio frequency transmission channel (1).
[0038] The broadband photonic de-skewing receiver link (2) includes: a laser (20), an electro-optic modulator (21), an optical filter (22), a first optical power divider (23), a delay fiber (24), a frequency shifting unit (25), a second optical power divider (26), and a detector (27). The detector (27) is a single photodetector. The frequency shifting unit (25) includes: an acousto-optic frequency shifter (251) and a microwave source (252). The laser (20), electro-optic modulator (21), optical filter (22), and first optical power divider (23) are connected in sequence. One input terminal of the electro-optic modulator (21) serves as the input terminal of the broadband photonic de-skewing receiver link (2) and is connected to the second amplifier. The output of (17) is connected; the output of the first optical power divider (23) is connected to the input of the delay fiber (24) and the first input of the acousto-optic frequency shifter (251), the output of the delay fiber (24) is connected to the input of the second optical power divider (26); the second input of the acousto-optic frequency shifter (251) is connected to the microwave source (252), the output of the acousto-optic frequency shifter (251) is connected to the input of the second optical power divider (26); the output of the second optical power divider (26) is connected to the input of the detector (27), and the output of the detector (27) is connected to the input of the digital demodulation parameter extraction unit (3) as the output of the broadband photon descrambling receiving link (2).
[0039] The aforementioned delay fiber (24) can be replaced by an adjustable fiber delay line.
[0040] The digital demodulation parameter extraction unit (3) includes an analog-to-digital converter (30), a digital demodulator (31), and an amplitude-phase fluctuation parameter extractor (32) connected in sequence. The input terminal of the analog-to-digital converter (30) is connected to the output terminal of the detector (27) as the input terminal of the digital demodulation parameter extraction unit (3), and the output terminal of the amplitude-phase fluctuation parameter extractor (32) is connected to the input terminal of the digital-to-analog converter (10) as the output terminal of the digital demodulation parameter extraction unit (3).
[0041] The workflow of the broadband RF transmission channel amplitude and phase fluctuation correction system in this embodiment is as follows: The digital-to-analog converter (10) generates a baseband LFM signal. The baseband LFM signal passes through the first filter (11) and then through the mixer (12) to be converted to an intermediate frequency. The intermediate frequency signal is filtered by the second filter (13) and then amplified by the first amplifier (14). After amplification, it is multiplied by the frequency multiplier (15) to the radio frequency operating frequency band. At this time, the bandwidth of the LFM signal is also expanded by multiple times. Finally, the broadband LFM signal is filtered and amplified by the third filter (16) and the second amplifier (17) and then output to the electro-optic modulator (21). The optical carrier output by the laser (20) is injected into the electro-optic modulator (21). The electro-optic modulator (21) modulates the radio frequency broadband LFM signal output by the broadband radio frequency transmission channel (1) into an optical carrier LFM signal. The bias voltage input is controlled to set the electro-optic modulator (21) to work at the zero bias point. At this time, the optical signal output by the electro-optic modulator (21) is a double-sideband carrier suppression signal. The double-sideband carrier suppression signal output by the electro-optic modulator (21) passes through the second filter (13) and then through the first amplifier (14) to be amplified by the second amplifier (15). The optical filter (22) filters out one sideband, and the remaining single-sideband carrier suppressed signal is split into two paths by the first optical power divider (23). The upper optical LFM signal is introduced into the transmission delay difference with the lower optical path through the delay fiber (24). The lower optical LFM signal is frequency-shifted by the acousto-optic frequency shifter (251), and the frequency shifting frequency is the frequency of the microwave signal loaded by the microwave source (252). The upper and lower optical signals are coherently combined by the second optical power divider (26), and the output is... The optical signal is injected into the detector (27) for photoelectric conversion; the analog-to-digital converter (30) collects the electrical signal after photoelectric conversion, and after the signal is demodulated by the digital demodulator (31), the LFM signal containing the channel amplitude and phase fluctuation parameters can be obtained. Then, the amplitude and phase fluctuation parameter extractor (32) performs orthogonal downconversion processing in the digital domain to extract the amplitude and phase fluctuation parameters carried by the distorted LFM signal, thereby generating digital predistortion channel correction parameters, which are sent to the broadband radio frequency transmission channel for transmission predistortion.
[0042] The signal demodulation process is as follows: The linear frequency modulated signal is modulated onto the optical carrier by an electro-optic modulator (21), which operates at a zero bias point. Taking a single-drive electro-optic modulator (21) as an example, the output optical signal can be expressed as:
[0043] In the formula, The amplitude of the light field. The optical carrier angular frequency, The modulator half-wave voltage, It is a radio frequency modulated signal. This is the modulator bias voltage; Radio frequency modulated signals can be represented as:
[0044] in, For the amplitude of the linear frequency modulated signal, The starting frequency of the linear frequency modulated signal. The frequency modulation slope is the instantaneous frequency of the linear frequency modulated signal. .
[0045] At the zero bias point, the bias voltage of the electro-optic modulator (21) is The optical carrier component in the output optical signal will be suppressed. The output optical signal of the electro-optic modulator (21) is filtered out by the optical filter (22) to remove the positive first-order modulation sideband. At this time, the output optical signal is simplified to:
[0046] in, It is a first-order Bessel function.
[0047] The single-sideband modulated optical signal is split into two paths by the first optical power divider (23), and the upper path is delayed by the delay fiber (24). The resulting optical field signal is represented as follows:
[0048] The lower path, via sound, light, and audio, introduces a frequency of... The microwave frequency-shifted optical field signal is represented as follows:
[0049] After being combined by the second optical power divider (26), the light field entering the detector (27) is:
[0050]
[0051]
[0052] The detector (27) converts the light field into an electrical signal output:
[0053]
[0054] in, The radio frequency output impedance of the detector (27) is denoted as the photoelectric conversion responsivity of the detector (27).
[0055] From the above equation, it can be seen that the signal after photon deskewing and photoelectric conversion has a frequency equal to The point frequency signal, in this embodiment, the delay difference between the two optical signals. The frequency of the point frequency signal is extremely small, so it is close to that of the frequency-shifted microwave signal source and is a low-frequency signal. It can be digitally acquired through a mature commercial analog-to-digital converter.
[0056] The electrical signal output by the detector (27) is acquired by the analog-to-digital converter (30) and then subjected to quadrature down-conversion in the digital domain to extract amplitude and phase information. The local oscillator frequency of the quadrature down-conversion is... The digitally demodulated signal is:
[0057] The above formula represents the digital zero-IF signal obtained after the ideal linear frequency modulated signal is corrected by the photon de-skewing receiver channel correction system.
[0058] Next, we consider the amplitude-phase nonlinear fluctuation problem in the broadband signal generation channel, assuming the amplitude-phase characteristics of the ideal system are as follows:
[0059] The amplitude and phase distortion of a real system can be decomposed into the sum of infinitely many simple harmonic distortions. The amplitude and phase characteristics of a system including distortion can be expressed as:
[0060] Its amplitude-frequency response revolves around a constant value It oscillates in a cosine manner, with phase frequency characteristics revolving around It oscillates in a sinusoidal manner; and These represent the amplitude and frequency of the amplitude-frequency response fluctuations, respectively. and These represent the amplitude and frequency of the phase frequency response fluctuations, respectively.
[0061] When an LFM signal passes through a distorted system, if the amplitude and phase distortion are slowly varying functions of frequency, then the output signal is equivalent to the product of the frequency domain distortion and the LFM signal, i.e.:
[0062] When the input linear frequency modulated signal contains system amplitude and phase distortion:
[0063] The amplitude fluctuation and phase fluctuation parameters are expressed as follows:
[0064]
[0065] The distorted LFM signal is injected into the photon de-chirping receiver channel correction system, and the complex intermediate frequency signal after digital demodulation is:
[0066] When the time difference When the signal amplitude is very small, if we approximate the first-order Bessel term in the signal amplitude with a small-signal approximation, then the amplitude term of the complex IQ signal is:
[0067] The above formula includes the system's amplitude-frequency response. .
[0068] The phase term of the complex IQ signal is:
[0069] in, The linear term, after being removed by linear fitting, leaves the following nonlinear term:
[0070] This reflects the instantaneous phase change caused by phase frequency fluctuations, i.e., the instantaneous frequency drift compared to an ideal linear frequency modulated signal. By accumulating and integrating the remaining nonlinear phase terms, the nonlinear phase error of the linear frequency modulated pulse can be obtained. That is, the phase frequency response of the system. .
[0071] In summary, by using photon deskewing reception and digital demodulation, the amplitude and phase fluctuation parameters of the transmission channel carried by the distorted LFM signal can be extracted, thereby generating digital predistortion channel correction parameters, which are then sent to the transmission channel for transmission predistortion.
[0072] Example 2 like Figure 2 The diagram shown is a structural block diagram of the broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on the photon deskewing receiver of the second embodiment of the present invention. Unlike the broadband radio frequency transmission channel amplitude and phase fluctuation correction system of the first embodiment, the detector (27) of this embodiment adopts a balanced photodetector. The use of a balanced photodetector can improve the signal-to-noise ratio of the receiver.
[0073] Example 3 like Figure 3The diagram shown is a structural block diagram of the broadband radio frequency transmission channel amplitude and phase ripple correction system of this embodiment of the present invention. Unlike the broadband radio frequency transmission channel amplitude and phase ripple correction system of embodiment one, a dual parallel modulator is used instead of an acousto-optic frequency shifter for optical frequency shifting, thereby achieving skew removal of the intermediate frequency signal. The frequency shifting unit (25) of this embodiment includes: a microwave source (252), a dual parallel modulator (253), a phase shifter (254), and a third power divider (255). The output end of the first optical power divider (23) is connected to the delay fiber. The input terminal of (24) is connected to the first input terminal of the dual parallel modulator (253), the output terminal of the microwave source (252) is connected to the input terminal of the third power divider (255), the output terminal of the third power divider (255) is connected to the input terminal of the phase shifter (254) and the second input terminal of the dual parallel modulator (253), the output terminal of the phase shifter (254) is connected to the third input terminal of the dual parallel modulator (253), and the output terminal of the dual parallel modulator (253) is connected to the input terminal of the second optical power divider (26).
[0074] The workflow of the broadband RF transmission channel amplitude and phase fluctuation correction system in this embodiment is as follows: The digital-to-analog converter (10) generates a baseband LFM signal. The baseband LFM signal passes through a first filter (11) and then through a mixer (12) to be converted to an intermediate frequency (IF). The IF signal is filtered by a second filter (13) and then amplified by a first amplifier (14). After amplification, it is multiplied by a frequency multiplier (15) to reach the radio frequency operating band. At this time, the bandwidth of the LFM signal is also multiplied. Finally, the broadband LFM signal is filtered and amplified by a third filter (16) and a second amplifier (17) and then output to an electro-optic modulator (21). The optical carrier output by the laser (20) is injected into the electro-optic modulator (21). In step 21), the broadband radio frequency LFM signal output from the broadband radio frequency transmitting channel (1) is modulated into an optical carrier LFM signal by the electro-optic modulator (21). The bias voltage input is controlled to set the electro-optic modulator (21) to work at the zero bias point. At this time, the optical signal output by the electro-optic modulator (21) is a double-sideband carrier suppression signal. The double-sideband carrier suppression signal output by the electro-optic modulator (21) is filtered out by the optical filter (22) to remove one sideband. The remaining single-sideband carrier suppression signal is split into two paths by the first optical power divider (23). The upper optical carrier LFM signal is introduced into the transmission of the lower optical path through the delay fiber (24). Due to the time delay, the downstream optical LFM signal is loaded by two microwave signals with the same amplitude but a 90° phase difference through a dual parallel modulator (253). The bias voltage of the dual parallel modulator (253) is set to single-sideband modulation mode. The optical signal output by the dual parallel modulator (253) is the frequency-shifted signal of the input optical signal, and the frequency shifting frequency is the frequency of the loaded microwave signal. The microwave signal output by the microwave source (252) is passed through the third power divider (255) and the phase shifter (254) to generate two microwave signals with the same amplitude but a 90° phase difference, which are respectively loaded onto the two sub-modulators of the dual parallel modulator (253). On the device, the optical signals of the upper and lower paths are coherently combined through a 2×2 proportional optical power divider, and the output optical signal is injected into the detector (27) for photoelectric conversion. The analog-to-digital converter (30) collects the electrical signal after photoelectric conversion, and after the signal is demodulated by the digital demodulator (31), the LFM signal containing the channel amplitude and phase fluctuation parameters can be obtained. Then, the amplitude and phase fluctuation parameter extractor (32) performs orthogonal downconversion processing in the digital domain to extract the amplitude and phase fluctuation parameters carried by the distorted LFM signal, thereby generating digital predistortion channel correction parameters, which are sent to the broadband radio frequency transmission channel for transmission predistortion.
[0075] Example 4 like Figure 4 The diagram shown is a structural block diagram of the broadband radio frequency transmission channel amplitude and phase fluctuation correction system of the present invention in embodiment four. Unlike the broadband radio frequency transmission channel amplitude and phase fluctuation correction system of embodiment three, the detector (27) of this embodiment adopts a balanced photodetector. The use of a balanced photodetector can improve the signal-to-noise ratio of the receiver.
[0076] Simulation test The simulation of amplitude and phase fluctuation correction parameters of broadband radio frequency transmission channel is carried out using the technical solution of the present invention. Figure 5(a) shows the set amplitude and phase nonlinear fluctuation parameters, and Figure 5(b) shows the demodulated amplitude and phase error information. As can be seen from the simulation results, the amplitude and phase nonlinear fluctuation parameters obtained by the technical solution of the present invention are basically consistent with the original settings. However, there are certain errors at the edge of the working frequency band due to the frequency response problem of the pulse signal edge.
[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon deskewing reception, characterized in that, include: A broadband radio frequency (RF) transmitting channel (1), a broadband photonic de-skewing receiving link (2), and a digital demodulation parameter extraction unit (3) are used. The input end of the broadband RF transmitting channel (1) is connected to the output end of the digital demodulation parameter extraction unit (3), the output end of the broadband RF transmitting channel (1) is connected to the input end of the broadband photonic de-skewing receiving link (2), and the output end of the broadband photonic de-skewing receiving link (2) is connected to the input end of the digital demodulation parameter extraction unit (3). The broadband RF transmitting channel (1) generates a broadband RF LFM signal, the broadband photonic de-skewing receiving link (2) converts the broadband RF LFM signal into a low-intermediate frequency point frequency signal for digital acquisition, and the digital demodulation parameter extraction unit (3) demodulates the transmission channel amplitude and phase fluctuation information carried in the broadband RF LFM signal to generate channel amplitude and phase correction parameters, and realizes broadband RF transmitting channel amplitude and phase fluctuation correction in a digital pre-distortion manner. The broadband photonic deskewing receiver link (2) includes: a laser (20), an electro-optic modulator (21), an optical filter (22), a first optical power divider (23), a delay fiber (24), a frequency shifting unit (25), a second optical power divider (26), and a detector (27); the laser (20), the electro-optic modulator (21), the optical filter (22), and the first optical power divider (23) are connected in sequence, and one input terminal of the electro-optic modulator (21) is connected to the output terminal of the second amplifier (17) as the input terminal of the broadband photonic deskewing receiver link (2); The output of the first optical power divider (23) is connected to the input of the delay fiber (24) and the input of the frequency shifting unit (25). The output of the delay fiber (24) is connected to the input of the second optical power divider (26). The output of the frequency shifting unit (25) is connected to the input of the second optical power divider (26). The output of the second optical power divider (26) is connected to the input of the detector (27). The output of the detector (27) is connected to the input of the digital demodulation parameter extraction unit (3) as the output of the broadband photonic deskewing receiving link (2). The digital demodulation parameter extraction unit (3) includes an analog-to-digital converter (30), a digital demodulator (31), and an amplitude-phase fluctuation parameter extractor (32) connected in sequence. The input end of the analog-to-digital converter (30) is connected to the output end of the detector (27) as the input end of the digital demodulation parameter extraction unit (3), and the output end of the amplitude-phase fluctuation parameter extractor (32) is connected to the input end of the digital-to-analog converter (10) as the output end of the digital demodulation parameter extraction unit (3).
2. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon de-skewing reception according to claim 1, characterized in that, The broadband radio frequency transmission channel includes a digital-to-analog converter (10), a first filter (11), a mixer (12), a second filter (13), a first amplifier (14), a frequency multiplier (15), a third filter (16), and a second amplifier (17) connected in sequence. The input terminal of the digital-to-analog converter (10) is connected to the output terminal of the digital demodulation parameter extraction unit (3) as the input terminal of the broadband radio frequency transmission channel (1), and the output terminal of the second amplifier (17) is connected to the input terminal of the broadband photon de-skewing receiving link (2) as the output terminal of the broadband radio frequency transmission channel (1).
3. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon de-skewing reception according to claim 1, characterized in that, The system's workflow is as follows: The digital-to-analog converter (10) generates a baseband LFM signal. The baseband LFM signal passes through a first filter (11) and then through a mixer (12) to be converted to an intermediate frequency (IF). The IF signal is filtered by a second filter (13) and then amplified by a first amplifier (14). After amplification, it is multiplied by a frequency multiplier (15) to reach the radio frequency operating frequency band. At this time, the bandwidth of the LFM signal is also multiplied. Finally, the broadband LFM signal is filtered and amplified by a third filter (16) and a second amplifier (17) and then output to an electro-optic modulator (21). The optical carrier output by the laser (20) is injected into the electro-optic modulator (21). The electro-optic modulator (21) transmits the broadband radio frequency LFM signal output from the broadband radio frequency transmission channel (1). The signal is modulated into an optical LFM signal; the bias voltage input is controlled, and the electro-optic modulator (21) is set to work at the zero bias point. At this time, the optical signal output by the electro-optic modulator (21) is a double-sideband carrier suppression signal. The double-sideband carrier suppression signal output by the electro-optic modulator (21) is filtered out by an optical filter (22) to remove one sideband. The remaining single-sideband carrier suppression signal is split into two paths by the first optical power divider (23). The upper optical LFM signal is introduced into the transmission delay difference with the lower optical path through the delay fiber (24). The lower optical LFM signal is frequency shifted by the frequency shifting unit (25). The upper and lower optical signals are coherently combined by the second optical power divider (26), and the output optical signal is injected into the detector (27) for photoelectric conversion. The analog-to-digital converter (30) collects the electrical signal after photoelectric conversion. After the signal is demodulated by the digital demodulator (31), the LFM signal containing the channel amplitude and phase fluctuation parameters can be obtained. Then, the amplitude and phase fluctuation parameter extractor (32) performs orthogonal downconversion processing in the digital domain to extract the amplitude and phase fluctuation parameters carried by the distorted LFM signal, thereby generating digital predistortion channel correction parameters, which are sent to the broadband radio frequency transmission channel for transmission predistortion.
4. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon de-skewing reception according to claim 3, characterized in that, The method for extracting the amplitude and phase fluctuation parameters carried by the distorted LFM signal is as follows: Let the local oscillator frequency of the quadrature downconversion be... The digitally demodulated signal is then: The above formula represents the digital zero-IF signal obtained after the ideal linear frequency modulated signal is corrected by the photon de-skewing receiver channel correction system; Let the amplitude and phase characteristics of the ideal system be: The amplitude-phase distortion of a real system can be decomposed into the sum of infinitely many simple harmonic distortions. The amplitude-phase characteristics of the system including distortion are expressed as follows: Its amplitude-frequency response revolves around a constant value It oscillates in a cosine manner, with phase frequency characteristics revolving around It oscillates in a sinusoidal manner; and These represent the amplitude and frequency of the amplitude-frequency response fluctuations, respectively. and These represent the amplitude and frequency of the phase frequency response fluctuations, respectively. When an LFM signal passes through a distorted system, if the amplitude and phase distortion are slowly varying functions of frequency, then the output signal is equivalent to the product of the frequency domain distortion and the LFM signal, i.e.: When the input linear frequency modulated signal contains system amplitude and phase distortion: The amplitude fluctuation and phase fluctuation parameters are expressed as follows: The distorted LFM signal is injected into the photon de-chirping receiver channel correction system, and the complex intermediate frequency signal after digital demodulation is: When the time difference When the signal amplitude is very small, if we approximate the first-order Bessel term in the signal amplitude with a small-signal approximation, then the amplitude term of the complex IQ signal is: The above formula includes the system's amplitude-frequency response. ; The phase term of the complex IQ signal is: in, The linear term, after being removed by linear fitting, leaves the following nonlinear term: The above equation gives the instantaneous phase change caused by phase frequency fluctuations, which is the instantaneous frequency drift compared to an ideal linear frequency modulated signal. Accumulating and integrating the remaining nonlinear phase terms yields the nonlinear phase error of the linear frequency modulated pulse. That is, the phase frequency response of the system. .
5. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon deskewing reception according to claim 1, characterized in that, The frequency shifting unit (25) includes: an acousto-optic frequency shifter (251) and a microwave source (252); the output end of the first optical power divider (23) is connected to the first input end of the acousto-optic frequency shifter (251), and the output end of the delay fiber (24) is connected to the input end of the second optical power divider (26); the second input end of the acousto-optic frequency shifter (251) is connected to the microwave source (252), and the output end of the acousto-optic frequency shifter (251) is connected to the input end of the second optical power divider (26).
6. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon de-skewing reception according to claim 1, characterized in that, The frequency shifting unit (25) includes: a microwave source (252), a dual parallel modulator (253), a phase shifter (254), and a third power divider (255); the output terminal of the first optical power divider (23) is connected to the first input terminal of the dual parallel modulator (253), the output terminal of the microwave source (252) is connected to the input terminal of the third power divider (255), the output terminal of the third power divider (255) is connected to the input terminal of the phase shifter (254) and the second input terminal of the dual parallel modulator (253), the output terminal of the phase shifter (254) is connected to the third input terminal of the dual parallel modulator (253), and the output terminal of the dual parallel modulator (253) is connected to the input terminal of the second optical power divider (26).
7. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon deskewing reception according to claim 1, characterized in that, The detector (27) is a single photodetector or a balanced photodetector.
8. The broadband radio frequency transmission channel amplitude and phase fluctuation correction system based on photon deskewing reception according to claim 1, characterized in that, The delay fiber (24) is replaced by an adjustable fiber delay line.