CN115603818A - Digital self-interference elimination device and method for optical frequency conversion and reference signal return - Google Patents

Abstract

The digital self-interference elimination device comprises a signal source (1) positioned at a base station A, an electric amplifier (2), a first electric power divider A (3), a transmitting antenna (4), a receiving antenna (5), a local vibration source (6), a second electric power divider B (7), a laser (8), a polarization controller (9) and a dual-polarization dual-drive Mach-Zehnder modulator (10); a single-mode optical fiber (15); an erbium-doped fiber amplifier (16), a polarization beam splitter (17), a first photoelectric detector A (18), a second photoelectric detector B (19) and a digital signal processor DSP (20) which are positioned at the central station B. The method for eliminating the digital self-interference under the condition of optical frequency conversion and reference signal simultaneous return in the in-band full-duplex ROF system is also provided. The invention converts the nonlinear problem into the linear problem for processing, thereby reducing the processing difficulty of the digital domain; the digital domain processing is carried out by using a high-digit ADC without realizing parameter tuning on an optical domain; the operation speed of the algorithm is greatly improved by using FTRLS multiplication.

Description

Digital self-interference elimination device and method for optical frequency conversion and reference signal return

technical field

The invention belongs to the technical field of microwave photon signal processing, and in particular relates to a digital self-interference elimination device and method for optical frequency conversion and simultaneous return of reference signals under an in-band full-duplex ROF system.

Background technique

Radio Frequency over Fiber (RoF) is a newly developed wireless access technology that combines photonic technology and wireless communication to meet the needs of high-speed and large-capacity wireless communication. Optical fiber has the characteristics of low loss, high bandwidth and anti-electromagnetic interference. As a transmission link, RoF technology has broad application prospects in the fields of wireless broadband communication, satellite communication, and intelligent transportation systems in the future. Faced with the current increasingly tight spectrum resources, the in-band full-duplex ROF system can ensure that the base station receives uplink signals from mobile users and sends downlink signals at the same time in the same frequency band, which improves the information throughput and doubles the spectrum efficiency.

In the in-band full-duplex ROF system, the self-interference between the transmit and receive channels is an urgent problem to be solved at present. The pure optical domain self-interference cancellation scheme is limited in dealing with multipath, nonlinear and other issues, and the digital The effective combination of algorithms provides a strong support for self-interference cancellation with high frequency band, large bandwidth and low loss.

In recent years, microwave photons combined with digital algorithms to achieve self-interference cancellation has been widely studied by domestic and foreign scientific research institutions. Among them, the focus is on the joint self-interference cancellation of microwave photon analog domain and nonlinear adaptive filtering digital domain for nonlinear and multipath effects. Scheme (1. Xiaolei, Yucheng, Zhang, et al. Optimized self-interference cancellation based on optical dual-parallel MZM for co-frequency and co-timefull duplex wireless communication under nonlinear distortion and emulated multipath effect[J]. Optics express, 2019, 27(26):37286-37297). Self-interference cancellation and signal of interest recovery using self-interference cancellation based on deep learning algorithm in wireless millimeter wave transmission system over optical fiber (2, ZhouQ, Shen S, Chen Y W, et al.Simultaneous nonlinear self-interference cancellation and signal of interest recovery using dual input deep neural network in new radio access networks [J]. Journal of Lightwave Technology, 2020, 39(7): 2046-2051.: 1297-1300). Literature (3, Zheng L, Liu Z, Xiao S, et al. Hybrid wideband multipath self-interference cancellation with an LMS pre-adaptive filter for in-bandfull-duplex OFDM signal transmission[J]. Optics Letters, 2020, 45(23 ): 6382) LMS is used as a pre-filter to match wireless multi-path self-interference signals, and eliminate them in the optical domain. Literature (4, Han M, Shi T, Chen Y. Digital-assisted photonic analog wideband multipath self-interference cancellation [J]. IEEE Photonics Technology Letters, 2022) uses RLS as a pre-filter to match weak multipath residual self-interference signals, After being synthesized with the main path reference signal, self-interference elimination and frequency down-conversion are realized in the optical domain.

However, the above scheme has certain limitations. Document 1 does not consider optical fiber transmission and down-conversion, and when the nonlinear component of the residual self-interference signal is strong, the complexity of the nonlinear adaptive filtering algorithm RLS-Vollterra is high; Document 2 when the power difference between the self-interference signal and the useful signal is large , the self-interference cancellation depth and the recovery ability of useful signals are limited; Documents 3 and 4 both use electrical delay lines for precise delay matching, and the uneven frequency response of electrical tuning devices for broadband signals will have a negative impact on algorithm performance. Influence, and the high-frequency pre-matching scheme needs to use a high-performance arbitrary waveform generator.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a digital self-interference cancellation device for optical frequency conversion and simultaneous return of reference signals in an in-band full-duplex ROF system, including a signal source 1 located at a base station A, an electrical amplifier 2, First electric power divider A3, transmitting antenna 4, receiving antenna 5, local oscillator source 6, second electric second electric power divider B7, laser 8, polarization controller 9, dual polarization dual drive Mach-Zehnder modulator 10 ; Single-mode optical fiber 15; Erbium-doped fiber amplifier 16, polarization beam splitter 17, first photodetector A18, second photodetector B19, digital signal processor DSP 20 located at central station B place; The driving Mach-Zehnder modulator 10 includes a first dual-driving Mach-Zehnder modulator A11, a second dual-driving Mach-Zehnder modulator B12, a 90-degree polarization rotator 13, and a polarization beam combiner 14;

At base station A:

The optical carrier generated by the laser 8 is input to the dual-polarization dual-drive Mach-Zehnder modulator 10 through the polarization controller 9;

The local oscillator source 6 generates a local oscillator signal and outputs it to the second electric second electric power divider B7, and the second electric second electric power divider B7 performs power distribution on the local oscillator signal ④, and one output to the first dual-drive Mach-Zehnder modulation A11, another output to the second dual-drive Mach-Zehnder modulator B12;

The carrier modulation signal generated by the signal source 1 is amplified by the electric amplifier 2 and then output to the first electric power divider A3, and the first electric power divider A3 performs power distribution on it, and one of the outputs is used as a reference signal ② and the local oscillator source 6 via One local oscillator signal ④ generated by the second electric power splitter B7 is input to the first dual-drive Mach-Zehnder modulator A11 for electro-optic modulation to generate X polarization state optical signal E _x ; the other is output to the transmitting antenna 4 and then issue;

The self-interference signal ① transmitted through the multi-path self-interference channel and the remote useful signal ③ are received by the receiving antenna 5 to form a mixed signal. After that, the mixed signal and the local vibration source 6 are generated by the second electric power splitter B7. All vibration signals ④ are input to the second dual-drive Mach-Zehnder modulator B12 for electro-optical modulation, and the generated X polarization state optical signal passes through the 90-degree polarization rotator 13 and then outputs after changing the polarization state;

The optical carrier modulation signal output by the first dual-drive Mach-Zehnder modulator A11 and the optical carrier modulation signal output by the 90-degree polarization rotator 13, the two signals of different polarization states are combined at the polarization beam combiner 14 to form a polarization beam combining optical signal; the polarized beam combining optical signal is transmitted to the central station B through the single-mode optical fiber 15;

At central station B:

After being amplified by the erbium-doped fiber amplifier 16, the beam is split by the polarization beam splitter 17, and output to the first photodetector A18 and the second photodetector B19 respectively, and obtained after being beat at the first photodetector A18. The frequency-converted intermediate-frequency reference signal is beaten at the second photodetector B19 to obtain an optically-converted intermediate-frequency received signal, and both the intermediate-frequency reference signal and the intermediate-frequency received signal are input to the digital signal processor DSP 20 for digital signal processing.

参考信号②为

有用信号③为

本振信号④为It also provides a digital self-interference elimination method for optical frequency conversion and reference signal simultaneous return under the in-band full-duplex ROF system, which is based on the optical frequency conversion under the in-band full-duplex ROF system as claimed in claim 1, and the reference signal is simultaneously The backhaul digital self-interference cancellation device assumes that the self-interference signal ① is

The reference signal ② is

The useful signal ③ is

The local oscillator signal ④ is

其中V_SI、V_R、V_SOI、V_LO分别为自干扰信号①、本地参考信号②、有用信号③、本振信号④的电压，ω_SI、ω_R、ω_SOI、ω_LO分别为自干扰信号①、本地参考信号②、有用信号③、本振信号④的角频率，

分别为自干扰信号①、本地参考信号②、有用信号③、本振信号④的相位；

Among them, V _SI , VR , V _SOI , and V _LO are voltages of self-interference signal ①, local reference signal ②, useful signal ③, and local oscillator signal ④ _respectively , and ω _SI , ω _R , ω _SOI , and ω _LO are self-interference Angular frequency of signal ①, local reference signal ②, useful signal ③, local oscillator signal ④,

are the phases of self-interference signal ①, local reference signal ②, useful signal ③, and local oscillator signal ④;

The method specifically includes the following steps:

At base station A:

Step 1: The carrier modulation signal generated by the signal source 1 is amplified by the electric amplifier 2 and then output to the first electric power divider A3, and the first electric power divider A3 performs power distribution on it, one of which outputs the reference signal ②; the other one The self-interference signal ① formed after being transmitted through the multi-path self-interference channel is received by the receiving antenna 5 together with the remote useful signal ③ to form a mixed signal (①+③);

Step 2: The laser 8 generates an optical carrier and the polarization controller 9 generates linearly polarized light, and the linearly polarized light is input to the dual-polarized dual-drive Mach-Zehnder modulator 10;

The reference signal ② and the local oscillator signal ④ generated by the local oscillator source 6 via the second electric power divider B7 are both input to the first dual-drive Mach-Zehnder modulator A11 for electro-optical modulation, and the first dual-drive Mach-Zehnder The Del modulator A11 is set to the minimum bias point, and outputs the X polarization state optical signal E _x ; the other output of the first electric power divider A3 is sent to the transmitting antenna 4 and sent by it;

The mixed signal (①+③) and another local oscillator signal ④ produced by the local oscillator source 6 through the second electric power divider B7 are all input to the second dual-drive Mach-Zehnder modulator B12 for electro-optical modulation, and the second dual The driving Mach-Zehnder modulator B12 is set to the minimum bias point, and the X polarization state optical signal output by the second dual driving Mach-Zehnder modulator B12 is rotated by the 90-degree polarization rotator 13 into a Y polarization state optical signal E _y ;

These two signals E _x and E _y of different polarization states are combined at the polarization beam combiner 14 to form a polarized light signal. The envelope E ₁ (t) of the polarized light signal is shown in Formula 1:

为光载波，E_c为光载波的幅度，ω_c为输入光载波频率，m_SI＝πV_SI/V_π、m_R＝πV_R/V_π、m_SOI＝πV_SOI/V_π、m_LO＝πV_LO/V_π分别为自干扰信号①、参考信号②、有用信号③、本振信号④的调制系数，V_π为双偏振双驱动马赫曾德尔调制器10的半波电压，J₀()、J₁()分别为0阶、1阶一类贝塞尔函数，t为时间；in,

is the optical carrier, E _c is the amplitude of the optical carrier, ω _c is the input optical carrier frequency, m _SI =πV _SI /V _π , m _R =πV _R /V _π , m _SOI =πV _SOI /V _π , m _LO = πV _LO /V _π are the modulation coefficients of the self-interference signal ①, reference signal ②, useful signal ③, and local oscillator signal ④ respectively, V _π is the half-wave voltage of the dual-polarization dual-drive Mach-Zehnder modulator 10, J ₀ () , J ₁ () are a class of Bessel functions of order 0 and order 1 respectively, and t is time;

Step 3: The bundled signal is transmitted to the central station B through the single-mode optical fiber 15; due to the dispersion effect of the optical fiber, the transmission function of the optical fiber is H(ω)=exp(-αL/2+jβ ₂ L(ω-ω _c ) ² /2), wherein α is an attenuation constant, β ₂ is a group velocity dispersion parameter, and L is an optical fiber length; therefore, the signal envelope E _SMF (t) of the output optical signal after passing through the single-mode optical fiber 15 is as shown in formula 2:

Wherein, E _SMFx and E _SMFy are respectively E _x and E _y obtained after transmission through the single-mode optical fiber 15 to obtain different polarization state optical signals;

At central station B:

Step 4: After the optical signal output by the single-mode optical fiber 15 is amplified by the erbium-doped fiber amplifier 16, it is split by the polarization beam splitter 17 and output to the first photodetector A18 and the second photodetector B19 respectively. Detector A18 place obtains the intermediate frequency reference signal through optical frequency conversion after beating frequency, obtains the intermediate frequency receiving signal through optical frequency conversion after beating frequency at the second photodetector B19 place; Intermediate frequency reference signal i _BPF1 (t), intermediate frequency receiving signal The formula of i _BPF2 (t) is as follows:

作为有用信号的幅度项，当本振信号和有用信号的频率相差不大时，能够保证中频有用信号受功率周期性衰落影响较小；Among them, G _OA is the amplification factor of the erbium-doped fiber amplifier, R ₁ and R ₂ are the responsivity of photodetector A18 and photodetector B19 respectively;

As the amplitude item of the useful signal, when the frequency difference between the local oscillator signal and the useful signal is not large, it can ensure that the intermediate frequency useful signal is less affected by the periodic power fading;

Step 5: Both the intermediate frequency reference signal and the intermediate frequency received signal are input to the digital signal processor DSP 20 for digital signal processing; so far, the intermediate frequency received signal includes self-interference signal and useful signal and the intermediate frequency reference signal is jointly transmitted to the central station, and the digital signal In the processor DSP 20, it is sampled and quantized by a high-digit ADC to the digital domain for further processing.

In one embodiment of the present invention, in the actual processing process, first stop sending useful signals according to the agreement, only receive self-interference signal ① and reference signal ② at the digital end, and use fast recursive least squares FTRLS to realize adaptive filtering, Minimize the error between the intermediate frequency self-interference signal and the intermediate frequency reference signal, and obtain the filter parameter value; then receive the useful signal transmitted by the remote end according to the agreement, and subtract the self-interference obtained by the intermediate frequency reference signal from the intermediate frequency reference signal through the filter to reconstruct the intermediate frequency received signal Signal, and finally obtain the useful signal of intermediate frequency, the useful signal is down-converted, the frequency deviation and phase deviation are recovered, and the useful signal is recovered after equalization.

The advantages of the present invention are as follows:

1. Self-interference signals pass through nonlinear devices such as electric amplifiers and modulators and multipath linear channels, and have complex linear/nonlinear components. Using digital baseband signals for nonlinear filtering or deep learning algorithms to eliminate nonlinear components will cause It brings great processing difficulty and algorithm calculation load, and the method of reference signal return transmits the nonlinear component of the reference signal back to the central station at the same time, transforms the nonlinear problem into a linear problem for processing, and reduces the processing in the digital domain difficulty.

2. Compared with the self-interference elimination scheme combining the optical domain with the digital domain, it is not necessary to realize parameter tuning in the optical domain, but using a high-digit ADC, such as a 12-bit ADC quantization error can reach a dynamic range of 72.25dB, which is a digital It is possible to realize the self-interference depth cancellation of large signals in the domain.

3. Due to the self-adaptive filtering of the self-interference signal with nonlinear components, it is necessary to set a longer filter length N to ensure the elimination depth of the self-interference signal, while the traditional recursive least squares RLS algorithm needs to bring O (N ² ) multiplication amount, while FTRLS's multiplication amount is only O(7N+14), which greatly improves the operation speed of the algorithm, and its most notable feature is that it does not need to perform matrix product operations.

Description of drawings

Figure 1 is a device diagram of a digital self-interference cancellation scheme based on optical frequency conversion and simultaneous return of reference signals under an in-band full-duplex ROF system;

Figure 2(a) is a comparison diagram before and after self-interference signal cancellation in 800MHz bandwidth, Figure 2(b) is a comparison diagram before self-interference signal cancellation and useful signal recovery in 400MHz bandwidth, and Figure 2(c) is a constellation diagram of the recovered useful signal.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

The present invention provides a digital self-interference elimination device for optical frequency conversion and simultaneous return of reference signals in an in-band full-duplex ROF system, including a signal source 1 located at a base station A, an electric amplifier 2, a first electric power divider A3, Transmitting antenna 4, receiving antenna 5, local oscillator source 6, second electric power divider B7, laser 8, polarization controller 9, dual polarization dual drive Mach-Zehnder modulator 10; single-mode optical fiber 15; located in the center Erbium-doped fiber amplifier 16, polarization beam splitter 17, first photodetector A18, second photodetector B19, digital signal processor DSP 20 at station B. Wherein, the dual-polarization dual-drive Mach-Zehnder modulator 10 includes a first dual-drive Mach-Zehnder modulator A11 , a second dual-drive Mach-Zehnder modulator B12 , a 90-degree polarization rotator 13 , and a polarization beam combiner 14 .

At base station A:

The optical carrier generated by the laser 8 is input to the dual-polarization dual-drive Mach-Zehnder modulator 10 through the polarization controller 9 .

The local oscillator source 6 generates a local oscillator signal and outputs it to the second electric second electric power divider B7, and the second electric second electric power divider B7 performs power distribution on the local oscillator signal ④, and one output to the first dual-drive Mach-Zehnder modulation device A11, and another output to the second dual-drive Mach-Zehnder modulator B12.

The carrier modulation signal generated by the signal source 1 is amplified by the electric amplifier 2 and then output to the first electric power divider A3, and the first electric power divider A3 performs power distribution on it, and one of the outputs is used as a reference signal ② and the local oscillator source 6 via One local oscillator signal ④ generated by the second electric power splitter B7 is input to the first dual-drive Mach-Zehnder modulator A11 for electro-optic modulation to generate X polarization state optical signal E _x ; the other is output to the transmitting antenna 4 and then issue.

The self-interference signal ① transmitted through the multi-path self-interference channel and the remote useful signal ③ are received by the receiving antenna 5 to form a mixed signal. After that, the mixed signal and the local vibration source 6 are generated by the second electric power splitter B7. All vibration signals ④ are input to the second dual-drive Mach-Zehnder modulator B12 for electro-optical modulation, and the generated X polarization optical signal passes through the 90-degree polarization rotator 13 and then outputs after changing the polarization state.

The optical carrier modulation signal output by the first dual-drive Mach-Zehnder modulator A11 and the optical carrier modulation signal output by the 90-degree polarization rotator 13, the two signals of different polarization states are combined at the polarization beam combiner 14 to form a polarization Combining light signals. The polarization-combined optical signal is transmitted to the central station B through the single-mode optical fiber 15 .

At central station B:

After being amplified by the erbium-doped fiber amplifier 16, the beam is split by the polarization beam splitter 17, and output to the first photodetector A18 and the second photodetector B19 respectively, and obtained after being beat at the first photodetector A18. The frequency-converted intermediate-frequency reference signal is beaten at the second photodetector B19 to obtain an optically-converted intermediate-frequency received signal, and both the intermediate-frequency reference signal and the intermediate-frequency received signal are input to the digital signal processor DSP 20 for digital signal processing.

A digital self-interference elimination method in which optical frequency conversion and reference signals are simultaneously returned in an in-band full-duplex ROF system is provided.

In the present invention, the self-interference elimination in the digital domain adopts the fast recursive least squares FTRLS algorithm, uses the intermediate frequency reference signal to filter out the self-interference signal in the intermediate frequency received signal, and finally realizes the recovery of the useful signal.

参考信号②为

有用信号③为

本振信号④为

其中V_SI、V_R、V_SOI、V_LO分别为自干扰信号①、本地参考信号②、有用信号③、本振信号④的电压，ω_SI、ω_R、ω_SOI、ω_LO分别为自干扰信号①、本地参考信号②、有用信号③、本振信号④的角频率，

分别为自干扰信号①、本地参考信号②、有用信号③、本振信号④的相位。For the convenience of explaining the frequency conversion and transmission of signals in the optical domain, regardless of factors such as nonlinearity and multipath, it is assumed that the self-interference signal ① is

The reference signal ② is

The useful signal ③ is

The local oscillator signal ④ is

Among them, V _SI , VR , V _SOI , and V _LO are voltages of self-interference signal ①, local reference signal ②, useful signal ③, and local oscillator signal ④ _respectively , and ω _SI , ω _R , ω _SOI , and ω _LO are self-interference Angular frequency of signal ①, local reference signal ②, useful signal ③, local oscillator signal ④,

They are the phases of the self-interference signal ①, the local reference signal ②, the useful signal ③, and the local oscillator signal ④ respectively.

At base station A:

Step 1: The carrier modulation signal generated by the signal source 1 is amplified by the electric amplifier 2 and then output to the first electric power divider A3, and the first electric power divider A3 performs power distribution on it, and one of the outputs is a reference signal ②. The self-interference signal ① and the remote useful signal ③ are received by the receiving antenna 5 together, forming a mixed signal (①+③).

Step 2: The laser 8 generates an optical carrier and the polarization controller 9 generates linearly polarized light, and the linearly polarized light is input to the dual-polarized dual-drive Mach-Zehnder modulator 10 .

The reference signal ② and the local oscillator signal ④ generated by the local oscillator source 6 via the second electric power divider B7 are both input to the first dual-drive Mach-Zehnder modulator A11 for electro-optical modulation, and the first dual-drive Mach-Zehnder The Del modulator A11 is set to the minimum bias point, and outputs the _X polarization state optical signal Ex . The other output of the first electric power divider A3 is sent to the transmitting antenna 4 and sent therefrom.

The mixed signal (①+③) and another local oscillator signal ④ produced by the local oscillator source 6 through the second electric power divider B7 are all input to the second dual-drive Mach-Zehnder modulator B12 for electro-optical modulation, and the second dual The driving Mach-Zehnder modulator B12 is set to the minimum bias point, and the X polarization state optical signal output by the second dual driving Mach-Zehnder modulator B12 is rotated by the 90-degree polarization rotator 13 into a Y polarization state optical signal E _y .

These two signals E _x and E _y of different polarization states are combined at the polarization beam combiner 14 to form a polarized light signal. The envelope E ₁ (t) of the polarized light signal is shown in Formula 1:

为光载波，E_c为光载波的幅度，ω_c为输入光载波频率，m_SI＝πV_SI/V_π、m_R＝πV_R/V_π、m_SOI＝πV_SOI/V_π、m_LO＝πV_LO/V_π分别为自干扰信号①、参考信号②、有用信号③、本振信号④的调制系数，V_π为双偏振双驱动马赫曾德尔调制器10的半波电压，J₀()、J₁()分别为0阶、1阶一类贝塞尔函数，t为时间；in,

is the optical carrier, E _c is the amplitude of the optical carrier, ω _c is the input optical carrier frequency, m _SI =πV _SI /V _π , m _R =πV _R /V _π , m _SOI =πV _SOI /V _π , m _LO = πV _LO /V _π are the modulation coefficients of the self-interference signal ①, reference signal ②, useful signal ③, and local oscillator signal ④ respectively, V _π is the half-wave voltage of the dual-polarization dual-drive Mach-Zehnder modulator 10, J ₀ () , J ₁ () are a class of Bessel functions of order 0 and order 1 respectively, and t is time;

Step 3: The bundled signal is transmitted to the central station B through the single-mode optical fiber 15 . Due to the dispersion effect of the fiber, the transmission function of the fiber is H(ω)=exp(-αL/2+jβ ₂ L(ω-ω _c ) ² /2), where α is the attenuation constant and β ₂ is the group velocity dispersion parameter , L is the fiber length. Therefore, the optical signal envelope E _SMF (t) output after the signal passes through the single-mode optical fiber 15 is shown in formula 2:

Wherein, E _SMFx and E _SMFy are respectively E _x and E _y to obtain optical signals with different polarization states after being transmitted through the single-mode optical fiber 15 .

At central station B:

Step 4: After the optical signal output by the single-mode optical fiber 15 is amplified by the erbium-doped fiber amplifier 16, it is split by the polarization beam splitter 17 and output to the first photodetector A18 and the second photodetector B19 respectively. After frequency beating at the detector A18, an intermediate frequency reference signal through optical frequency conversion is obtained, and after frequency beating at the second photodetector B19, an intermediate frequency receiving signal through optical frequency conversion is obtained. The formulas of intermediate frequency reference signal i _BPF1 (t) and intermediate frequency receiving signal i _BPF2 (t) are as follows:

作为有用信号的幅度项，当本振信号和有用信号的频率相差不大时，能够保证中频有用信号受功率周期性衰落影响较小。Wherein, G _OA is the amplification factor of the erbium-doped fiber amplifier, and R ₁ and R ₂ are the responsivity of the first photodetector A18 and the second photodetector B19 respectively.

As the amplitude item of the useful signal, when the frequency difference between the local oscillator signal and the useful signal is not large, it can ensure that the intermediate frequency useful signal is less affected by the periodic power fading.

Step 5: Both the intermediate frequency reference signal and the intermediate frequency received signal are input to the digital signal processor DSP 20 for digital signal processing. So far, the received intermediate frequency signal including self-interference signal, useful signal and intermediate frequency reference signal is transmitted to the central station B, and is sampled by a high-bit ADC in the digital signal processor DSP 20, quantized to the digital domain for further processing.

In the actual processing process, first stop sending useful signals according to the agreement, and only receive self-interference signal ① and reference signal ② at the digital end, using fast recursive least squares FTRLS (Dechene D J. "Fast transversalrecursive least-squares (FT- RLS) algorithm[C] "IEEE Trans Signal Proc. Citeseer, 2007.) realizes adaptive filtering, minimizes the error between the intermediate frequency self-interference signal and the intermediate frequency reference signal, and obtains the filter parameter value. Then receive the useful signal transmitted by the remote end according to the agreement, and subtract the self-interference reconstruction signal obtained from the intermediate frequency reference signal through the filter from the intermediate frequency received signal, and finally obtain the intermediate frequency useful signal. The useful signal is down-converted, and the frequency offset and phase offset are restored. , the useful signal is restored after equalization. Down-conversion, frequency offset, phase offset recovery, and equalization techniques are well known to those skilled in the art and will not be repeated here.

The advantages of the present invention are as follows:

1. Self-interference signals pass through nonlinear devices such as electric amplifiers and modulators and multipath linear channels, and have complex linear/nonlinear components. Using digital baseband signals for nonlinear filtering or deep learning algorithms to eliminate nonlinear components will cause It brings great processing difficulty and algorithm calculation load, and the method of reference signal return transmits the nonlinear component of the reference signal back to the central station at the same time, transforms the nonlinear problem into a linear problem for processing, and reduces the processing in the digital domain difficulty.

2. Compared with the self-interference elimination scheme combining the optical domain with the digital domain, it is not necessary to realize parameter tuning in the optical domain, but using a high-digit ADC, such as a 12-bit ADC quantization error can reach a dynamic range of 72.25dB, which is a digital It is possible to realize the self-interference depth cancellation of large signals in the domain.

3. Due to the self-adaptive filtering of the self-interference signal with nonlinear components, it is necessary to set a longer filter length N to ensure the elimination depth of the self-interference signal, while the traditional recursive least squares RLS algorithm needs to bring O (N ² ) multiplication amount, while FTRLS's multiplication amount is only O(7N+14), which greatly improves the operation speed of the algorithm, and its most notable feature is that it does not need to perform matrix product operations.

In order to verify the multipath, non-linear self-interference signal elimination ability of the present invention, and the recovery ability of the useful signal, the simulation is carried out by using optisystem14.0 and matlab2021b.

初始值均为0.00001。经过上述过程，方案的消除性能分别如下：Set self-jamming signal as QAM modulation signal, frequency 12.5GHz, bandwidth 800MHz, power 30dBm, local oscillator signal frequency 10GHz, power 27dBm, useful signal 16QAM signal, frequency 12.5GHz, bandwidth 400M, power -3dBm, self-jamming channel by 5 Paths with different delays and attenuations, the delays are [3, 30, 70, 80, 103] ps, the attenuations are [8, 10, 12, 13, 16] dB, the wavelength of the light source is 1550nm, and the power is 16dBm, linewidth 0.1MHz, Mach-Zehnder modulator extinction ratio 30dB, single-mode fiber length 10km, reference wavelength 1552nm, erbium-doped fiber amplifier gain 10dB, noise figure 4.5dB, polarization beam splitter offset The amount is 2°, the responsivity of photodetector A is 0.9A/W, and the responsivity of photodetector B is 0.85A/W. In the FTRLS algorithm, the filter order N is 800, the forgetting factor λ=1, and the forward/backward prediction minimum weighted square error

The initial value is 0.00001. After the above process, the elimination performance of the scheme is as follows:

Figure 2(a) is the spectrum diagram before and after self-interference cancellation. When the useful signal is not transmitted, the self-interference signal can reach a cancellation depth of 48dB, and the nonlinear components in the self-interference signal are also eliminated; Figure 2(b) is the self-interference signal The spectrum diagram of the interference signal and the restored useful signal. When the useful signal is transmitted, the useful signal can be recovered from the received signal. It can be seen from the figure that the elimination performance is slightly reduced, mainly because the self-interfering signal and the useful signal pass through together The amplitude of the self-interference signal obtained after the optical link beat frequency is slightly smaller than the amplitude obtained by the self-interference signal through the optical link beat frequency alone, which causes errors when recovering the useful signal from the received signal in the digital domain; secondly, through Fig. 2(a )(b) shows that the self-interfering signal, useful signal and reference signal can be optically converted to an intermediate frequency with a center frequency of 2.5 GHz; Figure (c) is the constellation diagram of the recovered 16QAM useful signal, and the EVM has reached 7.18% .

Claims (3)

1. A digital self-interference elimination device with optical frequency conversion and reference signal simultaneous return under an in-band full-duplex ROF system is characterized by comprising a signal source (1) positioned at a base station A, an electric amplifier (2), a first electric power divider A (3), a transmitting antenna (4), a receiving antenna (5), a local oscillation source (6), a second electric power divider B (7), a laser (8), a polarization controller (9) and a dual-polarization dual-drive Mach-Zehnder modulator (10); a single mode optical fiber (15); an erbium-doped fiber amplifier (16), a polarization beam splitter (17), a first photoelectric detector A (18), a second photoelectric detector B (19) and a digital signal processor DSP (20) which are positioned at the central station B; wherein, the dual-polarization dual-drive Mach-Zehnder modulator (10) comprises a first dual-drive Mach-Zehnder modulator A (11), a second dual-drive Mach-Zehnder modulator B (12), a 90-degree polarization rotator (13) and a polarization beam combiner (14);

at base station a:

an optical carrier generated by a laser (8) is input to a dual-polarization dual-drive Mach-Zehnder modulator (10) through a polarization controller (9);

the local oscillation source (6) generates a local oscillation signal and outputs the local oscillation signal to the second electric power divider B (7), the second electric power divider B (7) distributes the power of the local oscillation signal (4), one path of local oscillation signal is output to the first double-drive Mach-Zehnder modulator A (11), and the other path of local oscillation signal is output to the second double-drive Mach-Zehnder modulator B (12);

a carrier modulation signal generated by a signal source (1) is amplified by an electrical amplifier (2) and then output to a first electrical power divider A (3), the first electrical power divider A (3) distributes power, one output is used as a reference signal (2) and one local oscillation signal (4) generated by a local oscillation source (6) through a second electrical power divider B (7) are input to a first double-drive Mach-Zehnder modulator A (11) for electro-optical modulation, and an X polarization state optical signal E is generated _x (ii) a The other path is output to a transmitting antenna (4) and is transmitted by the transmitting antenna;

the self-interference signal (1) transmitted by a multipath self-interference channel and a far-end useful signal (3) are received by a receiving antenna (5) together to form a mixed signal, then the mixed signal and another local oscillation signal (4) generated by a local oscillation source (6) through a second electric power divider B (7) are input to a second double-drive Mach-Zehnder modulator B (12) for electro-optical modulation, and the generated X polarization state optical signal is output after the polarization state is changed through a 90-degree polarization rotator (13);

the light carrier modulation signal output by a first double-drive Mach-Zehnder modulator A (11) and the light carrier modulation signal output by a 90-degree polarization rotator (13) are combined at a polarization beam combiner (14) to form a polarization combined light signal; the polarized beam combination optical signal is transmitted to a central station B through a single mode optical fiber (15);

at central station B:

the mixed signal is amplified by an erbium-doped fiber amplifier (16), split by a polarization beam splitter (17), and respectively output to a first photoelectric detector A (18) and a second photoelectric detector B (19), an intermediate frequency reference signal subjected to optical frequency conversion is obtained at the first photoelectric detector A (18) after beat frequency, an intermediate frequency receiving signal subjected to optical frequency conversion is obtained at the second photoelectric detector B (19) after beat frequency, and the intermediate frequency reference signal and the intermediate frequency receiving signal are both input to a digital signal processor DSP (20) for digital signal processing.

2. A digital self-interference elimination method for optical frequency conversion and reference signal simultaneous return under an in-band full-duplex ROF system, which is based on the digital self-interference elimination device for optical frequency conversion and reference signal simultaneous return under the in-band full-duplex ROF system as claimed in claim 1, and assumes that the self-interference signal (1) is

The reference signal (2) is

The useful signal (3) is

The local oscillator signal (4) is

Wherein V _SI 、V _R 、V _SOI 、V _LO Respectively, the voltages of the self-interference signal (1), the local reference signal (2), the useful signal (3) and the local oscillator signal (4), omega _SI 、ω _R 、ω _SOI 、ω _LO Respectively are angular frequencies of a self-interference signal (1), a local reference signal (2), a useful signal (3) and a local oscillator signal (4),

the phase positions of the self-interference signal (1), the local reference signal (2), the useful signal (3) and the local oscillator signal (4) are respectively;

the method is characterized by comprising the following steps:

at base station a:

step 1: a carrier modulation signal generated by a signal source (1) is amplified by an electric amplifier (2) and then output to a first electric power divider A (3), the first electric power divider A (3) distributes power to the carrier modulation signal, and one path of output is a reference signal (2); the other path of self-interference signal (1) formed after being transmitted through a multipath self-interference channel is received by a receiving antenna (5) together with a far-end useful signal (3) to form a mixed signal ((1) + (3));

step 2: a laser (8) generates an optical carrier, a polarization controller (9) generates linearly polarized light, and the linearly polarized light is input to a dual-polarization dual-drive Mach-Zehnder modulator (10);

a reference signal (2) and one local oscillation signal (4) generated by a local oscillation source (6) through a second electric power divider B (7) are input to a first double-drive Mach-Zehnder modulator A (11) for electro-optical modulation, the first double-drive Mach-Zehnder modulator A (11) is set as a minimum bias point, and an X polarized optical signal E is output _x (ii) a The other path of the first power divider A (3) is output to a transmitting antenna (4) and transmitted by the transmitting antenna;

the mixed signal ((1) + (3)) and the other local oscillation signal (4) generated by the local oscillation source (6) through the second electric power divider B (7) are input to the second double-drive Mach-Zehnder modulator B (12) for electro-optical modulation, similarly, the second double-drive Mach-Zehnder modulator B (12) is set as a minimum offset point, and the signal is rotated into a Y-polarized optical signal E through a 90-degree polarization rotator (13) to form an X-polarized optical signal output by the second double-drive Mach-Zehnder modulator B (12) _y ；

The two signals E with different polarization states _x 、E _y Combining the beams at a polarization beam combiner (14) to form a polarized light signal, the polarized light signal enveloping E ₁ (t) is shown in equation 1:

wherein,

being optical carriers, E _c Amplitude of the optical carrier, ω _c For input light carrier frequency, m _SI ＝πV _SI /V _π 、m _R ＝πV _R /V _π 、m _SOI ＝πV _SOI /V _π 、m _LO ＝πV _LO /V _π The modulation coefficients are respectively self-interference signal (1), reference signal (2), useful signal (3) and local oscillator signal (4), V _π Is the half-wave voltage, J, of the dual-polarization dual-drive Mach-Zehnder modulator (10) ₀ ()、J ₁ () The first-class Bessel functions are 0-order and 1-order respectively, and t is time;

and step 3: the combined beam signal is transmitted to a central station B through a single mode optical fiber (15); due to the dispersion effect of the optical fiber, the transmission function of the optical fiber is H (omega) = exp (-alpha L/2+ j beta) ₂ L(ω-ω _c ) ² /2), where α is the damping constant, β ₂ Is a group velocity dispersion parameter, L is the fiber length; so that the signal passes through the single-mode fiber (15) and the output optical signal envelope E _SMF (t) is shown in equation 2:

wherein E is _SMFx 、E _SMFy Are respectively E _x 、E _y Different polarized optical signals are obtained after the transmission of the single mode optical fiber (15);

at the central station B:

and 4, step 4: an optical signal output by a single mode fiber (15) is amplified by an erbium-doped fiber amplifier (16), split by a polarization beam splitter (17), and output to a first photoelectric detector A (18) and a second photoelectric detector B (19) respectively, an intermediate frequency reference signal subjected to optical frequency conversion is obtained at the first photoelectric detector A (18) after beat frequency, and an intermediate frequency receiving signal subjected to optical frequency conversion is obtained at the second photoelectric detector B (19) after beat frequency; intermediate frequency reference signal i _BPF1 (t) intermediate frequency received signal i _BPF2 The formula (t) is as follows:

wherein G is _OA For amplification factor, R, of an erbium-doped fiber amplifier ₁ 、R ₂ Responsivity of a first photoelectric detector A (18) and responsivity of a second photoelectric detector B (19) are respectively measured;

as the amplitude term of the useful signal, when the frequency difference between the local oscillation signal and the useful signal is not large, the intermediate frequency useful signal can be ensured to be less influenced by power periodic fading;

and 5: the intermediate frequency reference signal and the intermediate frequency receiving signal are both input into a digital signal processor DSP (20) for digital signal processing; so far, the intermediate frequency receiving signal comprises a self-interference signal, a useful signal and an intermediate frequency reference signal which are transmitted to a central station B together, and the signal is sampled and quantized to a digital domain through a high-bit ADC in a digital signal processor DSP (20) for further processing.

3. The method for eliminating digital self-interference under optical frequency conversion and reference signal simultaneous return in the in-band full-duplex ROF system according to claim 2, characterized in that in the actual processing process, firstly, the sending of the useful signal is stopped according to convention, only the self-interference signal (1) and the reference signal (2) are received at the digital end, and the self-adaptive filtering is realized by using the fast recursive least squares (FTRLS), so that the error between the intermediate frequency self-interference signal and the intermediate frequency reference signal is minimized, and the filter parameter value is obtained; and then receiving a useful signal transmitted by a far end according to a convention, subtracting a self-interference reconstruction signal obtained by an intermediate frequency reference signal through a filter from the intermediate frequency received signal to finally obtain an intermediate frequency useful signal, and recovering the useful signal after down-conversion, frequency offset and phase offset equalization.

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