Image rejection mixing device and method with in-band self-interference cancellation capability

Abstract

The application discloses a mirror suppression mixing device with in-band self-interference cancellation capability, wherein a central station comprises a signal processing module, a 90-degree electrical coupler a, a photodetector x, a photodetector y, a polarization beam splitter and an optical power amplifier; a transmission medium is a single-mode optical fiber; a remote base station comprises a laser, a polarization controller, a polarization multiplexing-double drive-Mach-Zehnder modulator, an optical filter, a receiving antenna, a transmitting antenna, a direct current source x, a direct current source y, an electrical beam splitter a and an electrical beam splitter b, an electrical beam combiner a and an electrical beam combiner b, a 90-degree electrical coupler b, a local oscillator signal generator, an electrical attenuator and an electrical delay line. The application also provides a mirror suppression mixing method with in-band self-interference cancellation capability. The application not only can play the high spectral efficiency advantage of the in-band full duplex system, but also is not affected by the dispersion-induced power periodic fading phenomenon caused by optical fiber transmission, can effectively eliminate self-interference signals under the in-band full duplex system, and can effectively suppress the mirror interference caused by the open channel reception.

Description

Technical Field

[0001] This invention relates to the field of microwave photonic signal processing, specifically to an image suppression mixer and method that is compatible with long-distance dispersion transmission under in-band full-duplex conditions based on polarization multiplexing and Hartley structure, and has in-band self-interference cancellation capability. Background Technology

[0002] In recent years, the development of microwave photonics technology has attracted widespread attention across various fields. Compared with traditional electrical technologies, microwave photonics offers better broadband operation and electromagnetic interference resistance, along with advantages such as small size, light weight, and compatibility with fiber optic transmission, thus reducing transmission loss. Microwave photonic mixers play a crucial role in frequency conversion, not only down-converting received high-frequency signals to intermediate frequencies (IF) to reduce the sampling rate requirements for subsequent analog-to-digital conversion and digital signal processing, but also up-converting useful signals to the desired high-frequency band for transmission. However, in practical applications, open wireless channels typically receive various signals from the environment, and artificially generated image signals significantly interfere with the mixer's conversion results. Since the image signal and the IF signal after RF conversion are in the same frequency band, they cannot be separated by filters, resulting in distortion of the information carried by the useful signal. Furthermore, to address the prominent contradiction between limited spectrum resources and ever-increasing data rates, in-band full-duplex systems that can transmit and receive signals at the same frequency simultaneously have become a focus of attention due to their doubling of spectrum utilization efficiency. However, in-band full-duplex systems also introduce self-interference problems. High-power transmitted signals can crosstalk into the receiving channel, affecting the recovery of low-power received signals. This in-band self-interference cannot be eliminated using filters. Therefore, developing a mirror suppression mixer with self-interference cancellation capabilities is crucial for effectively solving the self-interference and mirror interference problems in in-band full-duplex systems, achieving efficient signal transmission and reception, and effective communication.

[0003] Traditional image rejection mixers are mostly based on the phase cancellation principle of the Hartley structure, introducing a phase difference between the image signal and the RF signal through phase shifters or 90° bridges. This method can still suppress image interference when the input frequency changes, which is beneficial to the wideband operation capability of the mixer. However, most current image rejection mixers do not take into account the elimination of self-interference signals, nor do they consider the impact of fiber dispersion on image rejection performance in long-distance fiber optic transmission scenarios. This prevents existing systems from fully utilizing the advantages of high spectral efficiency of in-band full-duplex systems and the high capacity and low transmission loss of RoF (RoF) systems. Furthermore, the independent functions of image rejection mixers and self-interference cancellation systems will increase system insertion loss, cost and complexity, and reduce flexibility. Therefore, there is an urgent need for an image rejection mixer that is compatible with in-band full-duplex systems and fiber optic transmission to solve the above problems. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides an image suppression mixer with in-band self-interference cancellation capability, comprising a remote base station, a transmission medium, and a central station;

[0005] The central station includes a signal processing module, a first 90° electrical coupler a 14, photodetectors x 12 and y 13, a polarization beam splitter 11, and an optical power amplifier 10; the transmission medium is single-mode optical fiber 9; the remote base station includes a laser 1, a polarization controller 2, a polarization multiplexing-dual-drive-Mach-Zehnder modulator PDM-DMZM 3, an optical filter 8, a receiving antenna 17, a transmitting antenna 18, a DC source x 15, a DC source y 16, a first electrical beam splitter a 19 and a second electrical beam splitter b 22, a first electrical beam combiner a 25 and a second electrical beam combiner b 26, a second 90° electrical coupler b 24, a local oscillator signal generator 23, an electrical attenuator 20, and an electrical delay line 21; wherein

[0006] Laser 1, the output of which is connected to the input of polarization controller 2;

[0007] Polarization controller 2 outputs a polarization-adjusted optical carrier.

[0008] The polarization multiplexing-dual-drive Mach-Zehnder modulator PDM-DMZM 3 is an integrated device that integrates sub-modulator x 4, sub-modulator y 5, 90° polarization rotator 6, and polarization beam combiner 7. The input terminal of PDM-DMZM 3 is connected to the output terminal of polarization controller 2, and outputs an optical radio frequency modulation signal.

[0009] Sub-modulator x 4 is embedded in the upper arm of PDM-DMZM 3, and its output is connected to one input of polarization combiner 7.

[0010] Sub-modulator y5 is embedded in the lower arm of PDM-DMZM 3, and its output is connected to the input of 90° polarization rotator 6.

[0011] The 90° polarization rotator 6 is embedded in the lower arm of the PDM-DMZM 3. Its input end is connected to the output end of the sub-modulator y 5, and its output end is connected to one input end of the polarization combiner 7.

[0012] The polarization combiner 7, integrated into the PDM-DMZM 3, receives the optical radio frequency modulation signal with polarization in the x-axis direction output by the sub-modulator x 4 and the optical radio frequency modulation signal with polarization in the y-axis direction output by the 90° polarization rotator 6. It combines the polarization orthogonal modulation signals of the upper and lower paths of the PDM-DMZM 3 and outputs the optical radio frequency modulation signal.

[0013] The optical filter 8 has its input end connected to the output end of the polarization beam combiner 7, and outputs a filtered optical radio frequency modulation signal.

[0014] The single-mode fiber 9 has its input end connected to the output end of the integrated optical filter 8, and its output is sent to the central station.

[0015] The input end of the optical power amplifier 10 is connected to the output end of the single-mode optical fiber 9.

[0016] The polarization beam splitter 11 has its input end connected to the output end of the optical power amplifier 10. It is used to separate two optical radio frequency modulation signals with orthogonal polarization and output an optical radio frequency modulation signal with x-axis polarization in the upper channel and an optical radio frequency modulation signal with y-axis polarization in the lower channel.

[0017] The photodetector x 12 has its input end connected to one output end of the polarization beam splitter 11, and outputs a photoelectric converted electrical signal.

[0018] The input end of the photodetector y 13 is connected to the other output end of the polarization beam splitter 11, and outputs another electrical signal after photoelectric conversion;

[0019] The first 90° electrical coupler a 14 has its input terminals connected to the output terminals of photodetectors x 12 and y 13 respectively, and outputs a coupled electrical signal.

[0020] A DC source x 15, the output of which is connected to the DC input of the upper branch sub-modulator x 4 of PDM-DMZM 3;

[0021] DC source y 16, whose output is connected to the DC input of PDM-DMZM 3 lower branch modulator y 5;

[0022] The receiving antenna 17 has its receiving end facing the wireless channel and its output end connected to the input end of the first electrical beam splitter a 19.

[0023] The first electrical beam splitter a 19 has its input terminal connected to the output terminal of the receiving antenna 17, and its output terminal connected to the RF input terminal x-1 of the upper branch sub-modulator x 4 and the RF input terminal y-1 of the lower branch sub-modulator y 5 of the PDM-DMZM 3, respectively.

[0024] The transmitting antenna 18 faces the wireless channel, and the transmitted signal will propagate in free space. The signal leaked from the transmitting antenna 18 into the receiving antenna 17 is the SI signal ③, and the signal returned from the transmitting antenna 18 to the electrical attenuator 20 is the reference signal (RI) ④.

[0025] Electrical attenuator 20 receives a reference signal (RI)④ from transmitting antenna 18, and its output is connected to the input of electrical delay line 21.

[0026] Electrical delay line 21 receives an amplitude-adjustable optical RI modulation signal from electrical attenuator 20, and its output is connected to the input of the second electrical beam splitter b 22.

[0027] The second electrical beam splitter b 22 receives an amplitude and delay-adjustable optical carrier RI modulation signal from the electrical delay line 21, and its output is connected to one of the inputs of the first electrical beam combiner a 25 and the second electrical beam combiner b 26, respectively.

[0028] The output terminal of the local oscillator signal generator 23 is connected to the input terminal of the second 90° electrical coupler b 24;

[0029] The second 90° electrical coupler b 24 receives the local oscillator (LO) signal ⑤ from the local oscillator signal generator 23, and its output terminal is connected to the other input terminal of the first electrical coupler a 25 and the second electrical coupler b 26 respectively.

[0030] The first electrical combiner a 25 has its output connected to another RF input x-2 of the upper branch sub-modulator x 4 of PDM-DMZM 3;

[0031] The output of the second electrical combiner b 26 is connected to another RF input y-2 of the lower branch modulator y 5 of PDM-DMZM 3.

[0032] A mirror suppression mixing method with in-band self-interference cancellation capability is also provided, which is based on the above-mentioned mirror suppression mixing device with in-band self-interference cancellation capability, wherein:

[0033] Assume that the optical carrier generated by laser 1 is E c (t)=E cexpjω c t, where E c It is the amplitude of the carrier wave, ω c This represents the angular frequency of the optical carrier wave; the SOI signal ① received by the receiving antenna 17 is... IM signal ② is SI signal ③ is The RI signal ④ transmitted back to the system device via transmitting antenna 18 is The LO signal ⑤ generated by the local oscillator signal generator 23 is Where V SOI V IM V SI V RI V LO The voltages ω for SOI, IM, SI, RI, and LO signals, respectively. SOI ω IM ω SI ω RI ω LO These are the angular frequencies of the SOI, IM, SI, RI, and LO signals, respectively. These represent the initial phases of the SOI, IM, SI, RI, and LO signals, respectively.

[0034] The method specifically includes the following steps:

[0035] (1) The optical carrier is generated by laser 1 and injected into PDM-DMZM 3;

[0036] The optical carrier generated by laser 1 is output to polarization controller 2, which adjusts the polarization state of the optical carrier to align with the principal x-axis of PDM-DMZM 3 and outputs it.

[0037] (2) The optical carrier output by polarization controller 2 is divided into two paths with equal power at the input of PDM-DMZM-3, and enters the upper sub-modulator x4 and the lower sub-modulator y5 respectively. At this time, the polarization states of the two optical carriers are the same.

[0038] (3) The optical carriers that enter PDM-DMZM 3 and are evenly divided into upper and lower paths are modulated by SOI signals, IM signals, SI signals, RI signals and LO signals in the upper and lower sub-modulators x 4 and y 5 respectively; as detailed below:

[0039] The SOI signal ①, IM signal ②, and SI signal ③ received by the receiving antenna 17 are divided into two paths with equal power and in the same direction by the first electrical beam splitter a 19. One path is injected into the first radio frequency input port x-1 of the upper sub-modulator x 4 of the PDM-DMZM 3 to modulate the upper optical carrier; the other path is injected into the first radio frequency input port y-1 of the lower sub-modulator y 4 of the PDM-DMZM 3 to modulate the lower optical carrier.

[0040] The RI signal ④ transmitted from the transmitting antenna 18 to the system device is first amplitude-tuned by the electrical attenuator 20, then delay-tuned by the electrical delay line 21, and then split into two paths with equal power and in the same direction by the second electrical beam splitter b 22. One path is combined with the I-path LO signal ⑤ generated by the local oscillator signal generator 23 and split by the second 90° electrical coupler b 24, and then injected into the second RF input port x-2 of the upper sub-modulator x 4 of the PDM-DMZM 3 to modulate the upper optical carrier. The other path is combined with the Q-path LO signal ⑤ generated by the local oscillator signal generator 23 and split by the second 90° electrical coupler b 24, and then injected into the second RF input port y-2 of the lower sub-modulator y 5 of the PDM-DMZM 3 to modulate the lower optical carrier.

[0041] The voltage of the DC source x 15 is set to V. π V π The half-wave voltage of PDM-DMZM3 is used to bias the upper sub-modulator x4 at the minimum transmission point through the DC input port x-3 of the upper branch of PDM-DMZM3, thereby introducing a π phase in both the upper and lower paths of the sub-modulator x4; the voltage of the DC source y16 is set to V. π Its function is to bias the lower sub-modulator y5 at the minimum transmission point through the DC input port y-3 of the lower branch of PDM-DMZM 3, and introduce the phase of π into the upper and lower paths of the lower sub-modulator y5.

[0042] The optical radio frequency modulation signals output by sub-modulator x4 and sub-modulator y5 have the same polarization state. At this time, the optical radio frequency modulation signal output by the lower sub-modulator y5 is polarized by the lower integrated 90° polarization rotator 6, so that the polarization state of the optical radio frequency modulation signal output by the 90° polarization rotator 6 is orthogonal to the polarization state of the optical radio frequency modulation signal output by sub-modulator x4, that is, the polarization is in the y-axis direction; the two orthogonally polarized optical radio frequency signals enter the polarization combiner 7 for polarization beam combining;

[0043] Therefore, the optical microwave signals at the output of PDM-DMZM 3 are as follows:

[0044]

[0045] Where β SOI =πV SOI / V π β IM =πV IM / V π β SI =πV SI / V π β RI =πV RI / V π and β LO =πV LO / V π These are the modulation coefficients for the SOI, IM, SI, RI, and LO signals, respectively, where j is an imaginary number, and V... π For the half-wave voltage of PDM-DMZM 3, e x and e y Let represent the unit vectors in the x and y polarization directions, respectively; after Bessel function expansion and retaining the first-order sidebands under small-signal modulation, we obtain:

[0046]

[0047] Where J0(β) i ), J1(β) i ) represents the 0th or 1st order Bessel function of the first kind corresponding to the signal, and i is represented as SOI\IM\SI\RI\LO;

[0048] (4) The optical microwave signal at the output of PDM-DMZM 3 enters the optical filter 8 to filter out the negative first-order sideband, retaining only the first-order sideband, and then leaves the remote base station for transmission through a single-mode optical fiber; specifically:

[0049] The transfer function of a single-mode fiber is expressed as:

[0050] H(jω)=exp[-αL / 2+jβ2L(ω-ω c ) 2 / twenty three)

[0051] Where α and L are the attenuation coefficient and length of the single-mode fiber, respectively, β2 is the second-order dispersion coefficient of the single-mode fiber, and ω represents the angular frequency of the signal passing through the single-mode fiber; the output signal after passing through optical filter 8 and single-mode fiber 9 is:

[0052]

[0053] in This represents the dispersive phase introduced by the single-mode fiber 9 at the angular frequency point ω; therefore, in equation (4), i is represented as SOI\IM\SI\RI\LO;

[0054] (5) The optical microwave signal, after long-distance transmission via single-mode fiber 9, enters the central station. After power amplification, polarization beam splitting and photoelectric conversion are achieved. Simultaneously, parameters are adjusted to suppress image interference signals and eliminate self-interference signals; specifically:

[0055] The optical microwave signal output from single-mode fiber 9 is amplified by optical power amplifier 10 and then injected into polarization beam splitter 11. Polarization beam splitter 11 separates the two orthogonally polarized optical microwave signals. The signal in the x-polarization direction enters photodetector x 12 for photoelectric conversion, and the signal in the y-polarization direction enters photodetector y 13 for photoelectric conversion. The electrical signals output by photodetector x 12 and photodetector y 13 are as follows:

[0056]

[0057] Where G is the optical field gain provided by optical amplifier 10, and R is the responsivity of photodetector x 12 and photodetector y 13, assuming that their responsivity is the same;

[0058] Subsequently, the two electrical signals output from photodetectors x 12 and y 13 enter the first 90° electrical coupler a 14. After introducing an additional 90° phase into the lower electrical signal, they are coupled into a single signal. Simultaneously, the electrical attenuator 20 and the electrical delay line 21 are adjusted so that the electrical signal generated after mixing the RI signal, SI signal, and local oscillator signal satisfies the following conditions. J0(β SOI )J0(β IM )J1(β SI )=J0(β LO )J1(β RI Under these two conditions, since the SI signal and the RI signal have the same frequency, the same transmission length through the same optical fiber, and the same dispersion value, it makes... Therefore, the amplitudes of the electrical signals generated after mixing the SI and RI signals with the local oscillator signal are equal, and the delay is matched. Thus, the output signal of the first 90° electro-coupler a14 is:

[0059]

[0060] Equation (6) shows that the mirror-image frequency conversion interference signal generated by the beat frequency of the IM signal and the LO signal is eliminated, and the self-interference signal generated by the beat frequency of the SI signal and the LO signal cancels out the reference signal generated by the beat frequency of the RI signal and the LO signal. Only the useful frequency conversion signal generated by the beat frequency of the SOI signal and the LO signal is retained in the output signal, and its frequency component is ω. SOI -ω LO The amplitude is -2GREc 2 J1(β SOI )J0(β IM )J0(β SI )J1(β LO )J0(β RI Furthermore, fiber optic transmission does not cause dispersion-induced periodic fading of the useful signal.

[0061] This invention not only leverages the high spectral efficiency of in-band full-duplex technology but also avoids the dispersion-induced power periodic fading caused by fiber optic transmission. It effectively eliminates self-interference signals in in-band full-duplex mode and suppresses image interference caused by human intervention or unintentional interference in open channel reception. The solution features a simple system structure, is compatible with long-distance fiber optic transmission, and separates remote base stations from the central station. This facilitates the transmission of received signals from multiple remote base stations to the central station via fiber optics for unified data processing, reducing the difficulty and structural complexity of base station signal processing. It effectively ensures the quality of received signals, improves system cost-effectiveness, and enhances overall system performance. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the image suppression mixer with in-band self-interference cancellation capability of the present invention. Specific implementation methods

[0063] The present invention will be further described below with reference to the accompanying drawings:

[0064] Figure 1 The image shown is an image suppression mixer compatible with long-distance dispersion transmission under in-band full-duplex conditions and possessing in-band self-interference cancellation capability. This device mainly consists of three parts: a remote base station, a transmission medium, and a central station. Specifically, it includes:

[0065] Laser 1, whose output is connected to the input of polarization controller 2, is used to provide a high-quality, low-phase-noise light source;

[0066] The polarization controller 2 is used to adjust the polarization state of the optical carrier so that the polarization state of the optical carrier input from the laser is aligned with one of the main axes (x-axis) of the polarization multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM) 3 and outputs the polarization-adjusted optical carrier.

[0067] The polarization multiplexing-dual-drive Mach-Zehnder modulator PDM-DMZM 3 is an integrated device that integrates sub-modulator x 4, sub-modulator y 5, 90° polarization rotator 6, and polarization beam combiner 7. The input terminal of PDM-DMZM 3 is connected to the output terminal of polarization controller 2, and is used to modulate the polarization-adjusted optical carrier and output the optical carrier radio frequency modulation signal.

[0068] Sub-modulator x 4, embedded in the upper arm of PDM-DMZM 3, is used to modulate the optical carrier of the upper branch and output an optical carrier radio frequency modulation signal polarized in the x-axis direction. Its output end is connected to one input end of polarization beam combiner 7.

[0069] Sub-modulator y5, embedded in the lower arm of PDM-DMZM 3, is used to modulate the optical carrier of the lower branch and output another optical carrier RF modulation signal polarized in the x-axis direction. Its output is connected to the input of 90° polarization rotator 6.

[0070] The 90° polarization rotator 6 is embedded in the lower arm of the PDM-DMZM 3. Its input end is connected to the output end of the sub-modulator y5, and its output end is connected to one input end of the polarization combiner 7. It is used to adjust the polarization state of the optical radio frequency modulation signal polarized in the x-axis direction of the lower branch, so that its output signal is in a polarization orthogonal state with the input signal, that is, the polarization state of the output signal is aligned with the y-axis and the optical radio frequency modulation signal polarized in the y-axis direction is output.

[0071] The polarization combiner 7, integrated into the PDM-DMZM 3, receives the optical radio frequency modulation signal with polarization in the x-axis direction output by the sub-modulator x 4 and the optical radio frequency modulation signal with polarization in the y-axis direction output by the 90° polarization rotator 6. It combines the polarization orthogonal modulation signals of the upper and lower paths of the PDM-DMZM 3 and outputs the optical radio frequency modulation signal.

[0072] Optical filter 8, whose input end is connected to the output end of polarization beam combiner 7, is used to filter the optical radio frequency modulation signal output by PDM-DMZM 3 and output the filtered optical radio frequency modulation signal, and select the required optical sideband.

[0073] The single-mode fiber 9, whose input end is connected to the output end of the integrated optical filter 8, is used to transmit the filtered optical radio frequency modulation signal from the remote base station to the central station.

[0074] The optical power amplifier 10 has its input end connected to the output end of the single-mode optical fiber 9 and is used to amplify the power of the optical radio frequency modulation signal transmitted through the optical fiber.

[0075] The polarization beam splitter 11 has its input end connected to the output end of the optical power amplifier 10. It is used to separate two optical radio frequency modulation signals with orthogonal polarization and output an optical radio frequency modulation signal with x-axis polarization in the upper channel and an optical radio frequency modulation signal with y-axis polarization in the lower channel.

[0076] The photodetector x 12 has its input end connected to one output end of the polarization beam splitter 11. It is used to perform photoelectric conversion on the optical radio frequency modulation signal in the x-axis polarization state and output a photoelectric converted electrical signal.

[0077] The photodetector y13 has its input end connected to the other output end of the polarization beam splitter 11. It is used to perform photoelectric conversion on the optical radio frequency modulation signal in the y-axis polarization state and output another photoelectric converted electrical signal.

[0078] The first 90° electrical coupler a 14 has its input terminals connected to the output terminals of photodetectors x 12 and y 13, respectively. It is used to introduce a 90° phase difference between the two output I / Q electrical signals and couple them to output the coupled electrical signal.

[0079] DC source x 15, whose output is connected to the DC input of sub-modulator x 4 on the upper branch of PDM-DMZM 3, is used to DC bias sub-modulator x 4;

[0080] DC source y16, whose output terminal is connected to the DC input terminal of sub-modulator y5 of the lower branch of PDM-DMZM 3, is used to DC bias sub-modulator y5.

[0081] The receiving antenna 17 has its receiving end facing the wireless channel and its output end connected to the input end of the first electrical beam splitter a 19. It is used to receive useful signals (SOI)①, image signals (IM)② and self-interference (SI) signals③ transmitted from the transmitting antenna 18 in the full-duplex system to free space and crosstalk to the receiving end.

[0082] The first electrical beam splitter a 19 has its input terminal connected to the output terminal of the receiving antenna 17, and its output terminal connected to the RF input terminal x-1 of the upper branch sub-modulator x 4 and the RF input terminal y-1 of the lower branch sub-modulator y 5 of the PDM-DMZM 3, respectively. It is used to split the mixed received signal with SI and IM signals into two signals with equal power and the same phase and output them separately.

[0083] The transmitting antenna 18 faces the wireless channel, and the transmitted signal will propagate in free space. The signal leaked from the transmitting antenna 18 into the receiving antenna 17 is the SI signal ③, and the signal returned from the transmitting antenna 18 to the electrical attenuator 20 is the reference signal (RI) ④.

[0084] The electrical attenuator 20 receives the reference signal (RI) ④ from the transmitting antenna 18, and its output is connected to the input of the electrical delay line 21. It is used to adjust the amplitude of the RI signal ④ and output an amplitude-adjustable optical RI modulation signal.

[0085] Electrical delay line 21 receives an amplitude-adjustable optical RI modulation signal from electrical attenuator 20, and its output is connected to the input of the second electrical beam splitter b 22. It is used to adjust the delay of the RI signal ④ and output an amplitude- and delay-adjustable optical RI modulation signal.

[0086] The second electrical beam splitter b 22 receives an amplitude and delay-adjustable optical RI modulation signal from the electrical delay line 21. Its output is connected to one of the inputs of the first electrical beam combiner a 25 and the second electrical beam combiner b 26, respectively, to split the amplitude and delay-adjusted RI signal into two optical RI modulation signals with equal power and the same phase and output them respectively.

[0087] The local oscillator signal generator 23 has its output terminal connected to the input terminal of the second 90° electrical coupler b 24, and is used to generate and output the local oscillator (LO) signal ⑤;

[0088] The second 90° electrical coupler b 24 receives the local oscillator (LO) signal ⑤ from the local oscillator signal generator 23. Its output terminal is connected to the other input terminal of the first electrical combiner a 25 and the second electrical combiner b 26, respectively, to split the LO signal ⑤ into two signals with equal power and orthogonal phase and output them respectively.

[0089] The first electrical combiner a 25 has its output connected to another RF input x-2 of the branch sub-modulator x 4 of PDM-DMZM 3. It is used to couple the I-channel LO signal from the second 90° electrical coupler b 24 and the RI signal from the second electrical splitter b 22 after amplitude and delay adjustment, so as to inject the coupled I-channel LO signal and the amplitude and delay adjusted RI signal into the sub-modulator x 4.

[0090] The output of the second electrical combiner b 26 is connected to another RF input y-2 of the lower branch sub-modulator y 5 of PDM-DMZM 3. It is used to couple the Q-channel LO signal from the 90° electrical coupler b-24 and the other amplitude and delay adjusted RI signal from the electrical beam splitter b-22 to obtain the coupled Q-channel LO signal and the amplitude and delay adjusted RI signal and inject them into the sub-modulator y 5.

[0091] The central station mainly includes a signal processing module, a first 90° electrical coupler a 14, two photodetectors (photodetector x 12 and photodetector y 13), a polarization beam splitter 11, and an optical power amplifier 10; the transmission medium mainly uses single-mode optical fiber 9; the remote base station includes a laser 1, a polarization controller 2, a polarization multiplexing-dual-drive-Mach-Zehnder modulator PDM-DMZM 3, an optical filter 8, a receiving antenna 17, a transmitting antenna 18, two DC sources (DC source x 15 and DC source y 16), two electrical beam splitters (first electrical beam splitter a 19 and second electrical beam splitter b 22), two electrical beam combiners (first electrical beam combiner a 25 and second electrical beam combiner b 26), a second 90° electrical coupler b 24, a local oscillator signal generator 23, an electrical attenuator 20, and an electrical delay line 21.

[0092] For ease of explanation, let's first assume that the optical carrier generated by laser 1 is E. c (t)=E c expjω c t, where E c It is the amplitude of the carrier wave, ω c This represents the angular frequency of the optical carrier wave. The SOI signal ① received by receiving antenna 17 is... IM signal ② is SI signal ③ is The RI signal ④ transmitted back to the system device via transmitting antenna 18 is The LO signal ⑤ generated by the local oscillator signal generator 23 is Where V SOI V IM V SI V RI V LO The voltages ω for SOI, IM, SI, RI, and LO signals, respectively. SOI ω IM ω SI ω RI ω LO These are the angular frequencies of the SOI, IM, SI, RI, and LO signals, respectively. These are the initial phases of the SOI, IM, SI, RI, and LO signals, respectively.

[0093] The image suppression mixing method of the present invention with in-band self-interference cancellation capability specifically includes the following steps:

[0094] (1) The optical carrier is generated by laser 1 and injected into PDM-DMZM 3;

[0095] The optical carrier generated by laser 1 is output to polarization controller 2. Polarization controller 2 adjusts the polarization state of the optical carrier to align with the main axis (x-axis) of PDM-DMZM 3 and outputs it.

[0096] (2) The optical carrier output by polarization controller 2 is divided into two paths with equal power at the input of PDM-DMZM-3, and enters the upper sub-modulator x4 and the lower sub-modulator y5 respectively. At this time, the polarization states of the two optical carriers are the same.

[0097] (3) The optical carriers that enter PDM-DMZM 3 and are evenly divided into upper and lower paths are modulated by SOI signals, IM signals, SI signals, RI signals and LO signals in the upper and lower sub-modulators x 4 and y 5 respectively; as detailed below:

[0098] The SOI signal ①, IM signal ②, and SI signal ③ received by the receiving antenna 17 are divided into two paths with equal power and in the same direction by the first electrical beam splitter a 19. One path is injected into the first radio frequency input port x-1 of the upper sub-modulator x 4 of the PDM-DMZM 3 to modulate the upper optical carrier; the other path is injected into the first radio frequency input port y-1 of the lower sub-modulator y 5 of the PDM-DMZM 3 to modulate the lower optical carrier.

[0099] The RI signal ④ transmitted from the transmitting antenna 18 to the system device is first amplitude-tuned by the electrical attenuator 20, then delay-tuned by the electrical delay line 21, and then split into two paths of equal power and in the same direction by the second electrical beam splitter b 22. One path is combined with the I-path LO signal ⑤ generated by the local oscillator signal generator 23 and split by the second 90° electrical coupler b 24, and then injected into the second RF input port x-2 of the upper sub-modulator x 4 of the PDM-DMZM 3 to modulate the upper optical carrier; the other path is combined with the Q-path LO signal ⑤ generated by the local oscillator signal generator 23 and split by the second 90° electrical coupler b 24, and then injected into the second RF input port y-2 of the lower sub-modulator y 5 of the PDM-DMZM 3 to modulate the lower optical carrier.

[0100] The voltage of the DC source x 15 is set to V. π (V π The voltage of PDM-DMZM 3 (half-wave voltage) is used to bias the upper sub-modulator x4 at the minimum transmission point through the DC input port x-3 of the upper branch of PDM-DMZM 3, thereby introducing a π phase in both the upper and lower paths of sub-modulator x4. The voltage of DC source y16 is set to V. πIts function is to bias the lower sub-modulator y5 at the minimum transmission point through the DC input port y-3 of the lower branch of PDM-DMZM 3, and introduce the phase of π into the upper and lower paths of the lower sub-modulator y5.

[0101] The optical radio frequency modulation signals output by sub-modulators x4 and y5 have the same polarization state. At this time, the optical radio frequency modulation signal output by the lower sub-modulator y5 is polarized by the integrated 90° polarization rotator 6, ensuring that the polarization state of the optical radio frequency modulation signal output by the 90° polarization rotator 6 is orthogonal to the polarization state of the optical radio frequency modulation signal output by sub-modulator x4, i.e., polarized in the y-axis direction. The two orthogonally polarized optical radio frequency signals then enter the polarization combiner 7 for polarization beam combining.

[0102] Therefore, the optical microwave signals at the output of PDM-DMZM 3 are as follows:

[0103]

[0104] Where β SOI =πV SOI / V π β IM =πV IM / V π β SI =πV SI / V π β RI =πV RI / V π and β LO =πV LO / V π These are the modulation coefficients for the SOI, IM, SI, RI, and LO signals, respectively, where j is an imaginary number, and V... π For the half-wave voltage of PDM-DMZM 3, e x and e y Let represent the unit vectors in the x and y polarization directions, respectively. After Bessel function expansion and preserving the first-order sidebands under small-signal modulation (β << 1), we obtain:

[0105]

[0106] Where J0(β) i ), J1(β) i )(i can be represented as SOI\IM\SI\RI\LO) is the 0th or 1st order Bessel function of the first kind corresponding to the signal.

[0107] (4) The optical microwave signal at the output of PDM-DMZM 3 enters the optical filter 8 to filter out the negative first-order sideband, retaining only the first-order sideband, and then leaves the remote base station for transmission via single-mode fiber. Specifically:

[0108] The transfer function of a single-mode fiber can generally be expressed as:

[0109] H(jω)=exp[-αL / 2+jβ2L(ω-ω c ) 2 / twenty three)

[0110] Where α and L are the attenuation coefficient and length of the single-mode fiber, respectively, β2 is the second-order dispersion coefficient of the single-mode fiber, and ω represents the angular frequency of the signal passing through the single-mode fiber. The output signal after passing through optical filter 8 and single-mode fiber 9 can be written as:

[0111]

[0112] in This represents the dispersive phase introduced into the single-mode fiber 9 at the angular frequency point ω. Therefore, in equation (4), i can be represented as SOI\IM\SI\RI\LO.

[0113] (5) The optical microwave signal, after long-distance transmission via single-mode fiber 9, enters the central station. After power amplification, polarization beam splitting and photoelectric conversion are achieved. Simultaneously, parameters are adjusted to suppress image interference signals and eliminate self-interference signals; specifically:

[0114] The optical microwave signal output from single-mode fiber 9 is amplified by optical power amplifier 10 and then injected into polarization beam splitter 11. Polarization beam splitter 11 separates the two orthogonally polarized optical microwave signals. The signal in the x-polarization direction enters photodetector x 12 for photoelectric conversion, and the signal in the y-polarization direction enters photodetector y 13 for photoelectric conversion. The electrical signals output by photodetector x 12 and photodetector y 13 are as follows:

[0115]

[0116] Where G is the optical field gain provided by optical amplifier 10, and R is the responsivity of photodetector x 12 and photodetector y 13, assuming that their responsivity is the same.

[0117] Subsequently, the two electrical signals output from photodetectors x 12 and y 13 enter the first 90° electrical coupler a 14. After introducing an additional 90° phase into the lower electrical signal, they are coupled into a single signal. Simultaneously, the electrical attenuator 20 and the electrical delay line 21 are adjusted so that the electrical signal generated after mixing the RI signal, SI signal, and local oscillator signal satisfies the following conditions. J0(β SOI )J0(β IM )J1(β SI )=J0(β LO )J1(β RI Under these two conditions, since the SI signal and the RI signal have the same frequency, the same transmission length through the same optical fiber, and the same dispersion value, it makes... Therefore, the amplitudes of the electrical signals generated after mixing the SI and RI signals with the local oscillator signal are equal, and the delay is matched. Thus, the output signal of the first 90° electro-coupler a14 is:

[0118]

[0119] Equation (6) shows that the mirror-image frequency conversion interference signal generated by the beat frequency of the IM signal and the LO signal is eliminated, and the self-interference signal generated by the beat frequency of the SI signal and the LO signal cancels out the reference signal generated by the beat frequency of the RI signal and the LO signal. Only the useful frequency conversion signal generated by the beat frequency of the SOI signal and the LO signal is retained in the output signal, and its frequency component is ω. SOI -ω LO The amplitude is -2GRE c 2 J1(β SOI )J0(β IM )J0(β SI )J1(β LO )J0(β RI Furthermore, fiber optic transmission does not cause dispersion-induced periodic fading of the useful signal.

[0120] Therefore, the output results guarantee the mixing function, enabling image rejection conversion of the input microwave signal and self-interference cancellation simultaneously. When the input frequency changes, the image rejection conversion condition can still be met. Self-interference cancellation can be achieved simply by adjusting the electrical attenuator and electrical delay line to meet the matching condition between the self-interference signal and the reference signal. Furthermore, due to single-sideband operation, the amplitude of the mixing signal is not affected by dispersion-induced power fading, ensuring the quality of the received signal.

[0121] This invention proposes a mirror suppression mixer and method with in-band self-interference cancellation capability. This device not only leverages the high spectral efficiency of in-band full-duplex operation but is also unaffected by dispersion-induced power periodic fading caused by fiber optic transmission. It effectively eliminates self-interference signals in in-band full-duplex mode and effectively suppresses image interference caused by human intervention or unintentional interference in open channel reception. This solution features a simple system structure, is compatible with long-distance fiber optic transmission, and separates remote base stations from the central station. This facilitates multiple remote base stations transmitting received signals to the central station via fiber optics for unified data processing, reducing the difficulty and structural complexity of base station signal processing. It effectively ensures the quality of received signals, improves system cost-effectiveness, and enhances overall system performance.

Claims

1. A mirror suppression mixer with in-band self-interference cancellation capability, comprising a remote base station, a transmission medium, and a central station; characterized in that: The central station includes a signal processing module, a first 90° electrical coupler a (14), photodetectors x (12) and y (13), a polarization beam splitter (11), and an optical power amplifier (10); the transmission medium is single-mode fiber (9); the remote base station includes a laser (1), a polarization controller (2), a polarization multiplexing-dual-drive-Mach-Zehnder modulator PDM-DMZM (3), an optical filter (8), a receiving antenna (17), a transmitting antenna (18), a DC source x (15), a DC source y (16), a first electrical beam splitter a (19) and a second electrical beam splitter b (22), a first electrical beam combiner a (25) and a second electrical beam combiner b (26), a second 90° electrical coupler b (24), a local oscillator signal generator (23), an electrical attenuator (20), and an electrical delay line (21); among which The laser (1) has its output end connected to the input end of the polarization controller (2); Polarization controller (2), which outputs a polarization-adjusted optical carrier; The polarization multiplexing-dual-drive Mach-Zehnder modulator PDM-DMZM(3) is an integrated device that integrates sub-modulator x(4), sub-modulator y(5), 90° polarization rotator (6) and polarization beam combiner (7). The input terminal of PDM-DMZM(3) is connected to the output terminal of polarization controller (2) to output an optical radio frequency modulation signal. Sub-modulator x (4) is embedded in the upper arm of PDM-DMZM (3), and its output is connected to one input of polarization combiner (7); The sub-modulator y(5) is embedded in the lower arm of the PDM-DMZM(3), and its output is connected to the input of the 90° polarization rotator (6). A 90° polarization rotator (6) is embedded in the lower arm of the PDM-DMZM (3). Its input end is connected to the output end of the sub-modulator y (5), and its output end is connected to one input end of the polarization combiner (7). The polarization combiner (7), integrated into the PDM-DMZM (3), receives the optical radio frequency modulation signal with polarization in the x-axis direction output by the sub-modulator x (4) and the optical radio frequency modulation signal with polarization in the y-axis direction output by the 90° polarization rotator (6), and combines the polarization orthogonal modulation signals of the upper and lower paths of the PDM-DMZM (3) and outputs the optical radio frequency modulation signal. The optical filter (8) has its input end connected to the output end of the polarization beam combiner (7) and outputs the filtered optical radio frequency modulation signal. A single-mode fiber (9) is connected at its input end to the output end of an integrated optical filter (8), and its output is sent to the central station. An optical power amplifier (10) has its input end connected to the output end of a single-mode optical fiber (9); The polarization beam splitter (11) has its input end connected to the output end of the optical power amplifier (10) and is used to separate two optical radio frequency modulation signals with orthogonal polarization and output the optical radio frequency modulation signal in the x-axis polarization state in the upper channel and the optical radio frequency modulation signal in the y-axis polarization state in the lower channel. The photodetector x(12) has its input end connected to one output end of the polarization beam splitter (11) and outputs a photoelectric converted electrical signal. The input end of the photodetector y(13) is connected to the other output end of the polarization beam splitter (11) to output another photoelectric converted electrical signal; The first 90° electrical coupler a(14) has its input terminals connected to the output terminals of photodetector x(12) and photodetector y(13) respectively, and outputs the coupled electrical signal. DC source x(15), whose output is connected to the DC input of the branch sub-modulator x(4) of PDM-DMZM(3); The DC source y(16) is connected to the DC input of the lower branch modulator y(5) of PDM-DMZM(3); The receiving antenna (17) has its receiving end facing the wireless channel and its output end connected to the input end of the first electrical beam splitter a (19). The first electrical beam splitter a (19) has its input end connected to the output end of the receiving antenna (17), and its output end is connected to the RF input end x-1 of the upper branch sub-modulator x (4) and the RF input end y-1 of the lower branch sub-modulator y (5) of the PDM-DMZM (3), respectively. The transmitting antenna (18) faces the wireless channel. The transmitted signal will propagate into free space. The signal leaked from the transmitting antenna (18) into the receiving antenna (17) is the SI signal ③. The signal transmitted back from the transmitting antenna (18) to the electrical attenuator (20) is the reference signal (RI) ④. An electrical attenuator (20) receives a reference signal (RI)④ from a transmitting antenna (18), and its output is connected to the input of an electrical delay line (21). Electrical delay line (21) receives an amplitude-adjustable optical RI modulation signal from electrical attenuator (20), and its output is connected to the input of second electrical beam splitter b (22). The second electrical beam splitter b (22) receives an amplitude and delay adjustable optical carrier RI modulation signal from the electrical delay line (21), and its output is connected to one of the inputs of the first electrical beam combiner a (25) and the second electrical beam combiner b (26). The local oscillator signal generator (23) has its output terminal connected to the input terminal of the second 90° electrical coupler b (24); The second 90° electrical coupler b (24) receives the local oscillator LO signal ⑤ from the local oscillator signal generator (23), and its output is connected to the other input of the first electrical coupler a (25) and the second electrical coupler b (26); The first electrical combiner a(25) has its output connected to another RF input x-2 of the branch sub-modulator x(4) of the PDM-DMZM(3); The output of the second electrical combiner b(26) is connected to another RF input y-2 of the lower branch modulator y(5) of PDM-DMZM(3).

2. A mirror suppression mixing method with in-band self-interference cancellation capability, based on the mirror suppression mixing device with in-band self-interference cancellation capability as described in claim 1, characterized in that: Assume the optical carrier generated by laser (1) is E c (t)=E c expjω c t, where E c It is the amplitude of the carrier wave, ω c The angular frequency of the optical carrier is represented; the SOI signal ① received by the receiving antenna (17) is IM signal ② is SI signal ③ is The RI signal ④ transmitted back to the system device via the transmitting antenna (18) is The LO signal ⑤ generated by the local oscillator signal generator (23) is Where V SOI V IM V SI V RI V LO The voltages ω of the SOI, IM, SI, RI, and LO signals, respectively. SOI ω IM ω SI ω RI ω LO These are the angular frequencies of the SOI, IM, SI, RI, and LO signals, respectively. These represent the initial phases of the SOI, IM, SI, RI, and LO signals, respectively. The method specifically includes the following steps: (1) The optical carrier is generated by laser (1) and injected into PDM-DMZM (3); The optical carrier generated by the laser (1) is output to the polarization controller (2), which adjusts the polarization state of the optical carrier to be aligned with the main axis x-axis of the PDM-DMZM (3) and outputs it. (2) The optical carrier output by the polarization controller (2) is divided into two paths with equal power at the input of PDM-DMZM (3), and enters the upper sub-modulator x (4) and the lower sub-modulator y (5) respectively. At this time, the polarization states of the two optical carriers are the same. (3) The optical carriers that enter the PDM-DMZM (3) and are evenly divided into upper and lower paths are modulated by SOI signal, IM signal, SI signal, RI signal and LO signal in the upper and lower sub-modulators x (4) and y (5) respectively; as follows: The SOI signal ①, IM signal ② and SI signal ③ received by the receiving antenna (17) are divided into two paths with equal power and in the same direction by the first electrical beam splitter a (19). One path is injected into the first radio frequency input port x-1 of the upper sub-modulator x (4) of the PDM-DMZM (3) to modulate the upper optical carrier; the other path is injected into the first radio frequency input port y-1 of the lower sub-modulator y (5) of the PDM-DMZM (3) to modulate the lower optical carrier. The RI signal ④ transmitted from the transmitting antenna (18) to the system device is first amplitude-tuned by the electrical attenuator (20), then delayed by the electrical delay line (21), and then split into two paths with equal power and in the same direction by the second electrical beam splitter b (22). One path is combined with the I-path LO signal ⑤ generated by the local oscillator signal generator (23) and split by the second 90° electrical coupler b (24) and then injected into the second RF input port x-2 of the upper sub-modulator x (4) of the PDM-DMZM (3) to modulate the upper optical carrier. The other path is combined with the Q-path LO signal ⑤ generated by the local oscillator signal generator (23) and split by the second 90° electrical coupler b (24) and then injected into the second RF input port y of the lower sub-modulator y (5) of the PDM-DMZM (3) by the second electrical beam combiner b (26). - 2. Injection, modulating the downstream optical carrier; The voltage of DC source x(15) is set to V. π V π The half-wave voltage of PDM-DMZM(3) is used to bias the upper sub-modulator x(4) at the minimum transmission point through the DC input port x-3 of the upper branch of PDM-DMZM(3), thereby introducing a phase of π in the upper and lower paths of the sub-modulator x(4); the voltage of the DC source y(16) is set to V. π Its function is to bias the lower sub-modulator y(5) at the minimum transmission point through the DC input port y-3 of the lower branch of PDM-DMZM(3), and introduce the phase of π in the upper and lower paths of the lower sub-modulator y(5). The optical radio frequency modulation signals output by sub-modulator x (4) and sub-modulator y (5) have the same polarization state. At this time, the optical radio frequency modulation signal output by the lower sub-modulator y (5) is polarized by the lower integrated 90° polarization rotator (6), so that the polarization state of the optical radio frequency modulation signal output by the 90° polarization rotator (6) is orthogonal to the polarization state of the optical radio frequency modulation signal output by the sub-modulator x (4), that is, the polarization is in the y-axis direction; the two orthogonally polarized optical radio frequency signals enter the polarization combiner (7) for polarization beam combining; Therefore, the optical microwave signals at the output of PDM-DMZM(3) are as follows: Where β SOI =πV SOI / V π β IM =πV IM / V π β SI =πV SI / V π β RI =πV RI / V π and β LO =πV LO / V π These are the modulation coefficients for the SOI, IM, SI, RI, and LO signals, respectively, where j is an imaginary number, and V... π For the half-wave voltage of PDM-DMZM(3), e x and e y Let represent the unit vectors in the x and y polarization directions, respectively; after Bessel function expansion and retaining the first-order sidebands under small-signal modulation, we obtain: Where J0(β) i ), J1(β) i ) represents the 0th or 1st order Bessel function of the first kind corresponding to the signal, and i is represented as SOI\IM\SI\RI\LO; (4) The optical microwave signal at the output of PDM-DMZM (3) enters the optical filter (8) to filter out the negative first-order sideband, retaining only the first-order sideband, and then leaves the remote base station for transmission through a single-mode optical fiber; specifically: The transfer function of a single-mode fiber is expressed as: H(jω)=exp[-αL / 2+jβ2L(ω-ω c ) 2 / 2] (3) Where α and L are the attenuation coefficient and length of the single-mode fiber, respectively, β2 is the second-order dispersion coefficient of the single-mode fiber, and ω represents the angular frequency of the signal passing through the single-mode fiber; the output signal after passing through the optical filter (8) and the single-mode fiber (9) is: in This is the dispersive phase introduced by the single-mode fiber (9) at the angular frequency point ω; therefore, in equation (4), i is represented as SOI\IM\SI\RI\LO; (5) The optical microwave signal, after long-distance transmission via single-mode fiber (9), enters the central station. After power amplification, polarization beam splitting and photoelectric conversion are achieved. At the same time, parameters are adjusted to suppress image interference signals and eliminate self-interference signals; specifically: The optical microwave signal output from the single-mode fiber (9) is amplified by the optical power amplifier (10) and injected into the polarization beam splitter (11). The polarization beam splitter (11) separates the two orthogonally polarized optical microwave signals. The signal in the x-polarization direction enters the photodetector x (12) for photoelectric conversion, and the signal in the y-polarization direction enters the photodetector y (13) for photoelectric conversion. The electrical signals output by photodetector x (12) and photodetector y (13) are respectively: Where G is the optical field gain provided by the optical power amplifier (10), and R is the responsivity of photodetector x (12) and photodetector y (13), assuming that the responsivity of the two is the same; Subsequently, the two electrical signals output from photodetector x (12) and photodetector y (13) enter the first 90° electrical coupler a (14). After introducing an additional 90° phase into the lower electrical signal, they are coupled into one signal. At the same time, the electrical attenuator (20) and the electrical delay line (21) are adjusted so that the electrical signal generated after mixing the RI signal, the SI signal and the local oscillator signal satisfies the following conditions. J0(β SOI )J0(β IM )J1(β SI )=J0(β LO )J1(β RI Under these two conditions, since the SI signal and the RI signal have the same frequency, the same transmission length through the same optical fiber, and the same dispersion value, it makes... Therefore, the amplitudes of the electrical signals generated after mixing the SI and RI signals with the local oscillator signal are equal, and the delay is matched. Thus, the output signal of the first 90° electrical coupler a(14) is: Equation (6) shows that the mirror-image frequency conversion interference signal generated by the beat frequency of the IM signal and the LO signal is eliminated, and the self-interference signal generated by the beat frequency of the SI signal and the LO signal cancels out the reference signal generated by the beat frequency of the RI signal and the LO signal. Only the useful frequency conversion signal generated by the beat frequency of the SOI signal and the LO signal is retained in the output signal, and its frequency component is ω. SOI -ω LO The amplitude is -2GRE c 2 J1(β SOI )J0(β IM )J0(β SI )J1(β LO )J0(β RI Furthermore, fiber optic transmission does not cause dispersion-induced periodic fading of the useful signal.

Images