Analog optical wireless MIMO transmission system and method based on pilot adaptive calibration

Abstract

The application provides an analog optical wireless MIMO transmission system and method based on pilot adaptive calibration. The system comprises a near-end access unit, a single-mode optical fiber transmission link and a far-end unit. The near-end access unit injects reference pilot signals with non-overlapping frequencies in the out-of-band protection frequency band of each analog radio frequency signal, and the signals are combined by a dense wavelength division multiplexing transmission module and then input into a single-mode optical fiber for transmission. The far-end unit restores the optical signals into analog radio frequency electrical signals and inputs the signals into an adaptive analog calibration network. A pilot feedback control loop extracts sampling signals from the output end of the network and filters out the reference pilot signals, compares the amplitude difference and phase difference of each channel, and generates a direct current control voltage. The direct current control voltage is fed back to the adaptive analog calibration network, which is used for reverse adjustment of the electrically controllable variable attenuator and the electrically controllable variable phase shifter. The application utilizes a pure analog hardware negative feedback mechanism to dynamically eliminate the imbalance between channels of a multiple-input multiple-output system.

Description

Technical Field

[0001] This invention relates to the field of analog optical wireless communication technology, specifically to an analog optical wireless MIMO transmission system and method based on pilot adaptive calibration. Background Technology

[0002] Analog optical wireless communication technology is a communication system that directly modulates radio frequency signals onto an optical carrier and transmits them through optical fiber. Multiple-input multiple-output (MIMO) technology utilizes multiple antennas to simultaneously transmit multiple spatial streams at both the transmitting and receiving ends, thereby increasing the system capacity of wireless communication. The analog optical wireless MIMO transmission system, which combines these two technologies, can solve the problems of high transmission loss and limited coverage associated with traditional high-frequency radio frequency coaxial cables.

[0003] In existing analog optical-over-wireless MIMO transmission systems, to ensure the independent transmission of multiple spatial stream signals, the conventional engineering implementation involves laying multiple parallel physical optical fibers between the near-end access device and the far-end device. Specifically, the transmitting end converts multiple independent radio frequency signals into electro-optical signals, and then injects them into their respective independent optical fibers for transmission. The receiving end then converts the optical signals transmitted independently from each fiber back into radio frequency signals and sends them to the corresponding multi-antenna array.

[0004] The existing transmission system suffers from the drawback of difficulty in maintaining a consistent physical transmission environment. Traditional solutions use multiple physical optical fibers to independently transmit multiple spatial stream signals. In actual engineering installation and operation, it is impossible to guarantee that the physical length of each fiber is absolutely equal. Small differences in fiber length will introduce uncontrollable optical path difference during radio frequency signal transmission, resulting in severe phase jitter and physical phase shift between channels when different spatial stream signals reach the far end. This undermines the fundamental condition of consistent underlying physical environment for multiple signal transmission in a multiple-input multiple-output system. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an analog optical wireless MIMO transmission system and method based on pilot adaptive calibration, which solves the problems of uncontrollable optical path difference and severe signal phase jitter caused by the inability to perfectly align the lengths of multiple physical optical fibers in analog optical wireless communication systems.

[0006] The first aspect of the present invention provides an analog optical wireless MIMO transmission system based on pilot adaptive calibration, including a near-end access unit, a single-mode fiber optic transmission link, and a far-end unit, wherein the near-end access unit is connected to the far-end unit through the single-mode fiber optic transmission link.

[0007] The near-end access unit includes a MIMO (Multiple-Input Multiple-Output) RF input module, a pilot injection module, and a DWDM (Dense Wavelength Division Multiplexing) transmitter module. The output of the MIMO RF input module is connected to the input of the pilot injection module. The pilot injection module injects a reference pilot signal into the out-of-band frequency band of each analog RF signal. The output of the pilot injection module is connected to the input of the DWDM transmitter module. The DWDM transmitter module controls semiconductor lasers of different wavelengths to convert the multiple analog signals after the injection of the reference pilot signal into optical signals, which are then combined via an optical combiner and input into a single-mode fiber optic transmission link.

[0008] The remote unit includes an optical demultiplexing module, a photodetector module, an adaptive analog calibration network, and a pilot feedback control loop. The output of the optical demultiplexing module is connected to the input of the photodetector module. The photodetector module converts each optical signal into an analog radio frequency (RF) signal containing wireless communication RF data signals and reference pilot signals. The adaptive analog calibration network is connected to the output of the photodetector module, and it connects an electrically controlled variable attenuator and an electrically controlled variable phase shifter in series in each RF channel.

[0009] The pilot feedback control loop extracts the sampled signal from the output of the adaptive analog calibration network and filters out the reference pilot signal. The loop calculates the amplitude and phase differences of the reference pilot signals for each channel and outputs a DC control voltage. This DC control voltage is fed back to the adaptive analog calibration network and input to the voltage control terminals of the electronically controlled variable attenuator and the electronically controlled variable phase shifter, respectively.

[0010] Preferably, the pilot injection module includes local analog oscillators and microstrip line directional couplers, the number of which is equal to the number of multiple-input multiple-output (MIMO) space streams. The signal input port of the microstrip line directional coupler is connected to the output port of the MIMO RF input module, and the coupling port of the microstrip line directional coupler is connected to the signal output port of the local analog oscillators. The microstrip line directional coupler superimposes the reference pilot signals generated by each local analog oscillator onto the corresponding analog RF signal to form a composite transmit signal. The frequencies of the various reference pilot signals do not overlap.

[0011] Preferably, the dense wavelength division multiplexing (DWDM) transmitter module includes a DWDM laser array and an optical combiner. The DWDM laser array comprises semiconductor lasers with a number equal to the number of multiple-input multiple-output (MIMO) spatial streams and different center wavelengths. Each composite transmission signal is independently input to the RF modulation input of its corresponding semiconductor laser. After electro-optical conversion, the signals are multiplexed and combined by the optical combiner into a single converged optical signal, which is then sent to a single-mode fiber optic transmission link for parallel transmission.

[0012] Preferably, the photodetector module integrates an equal number of independent photodetectors as the number of multiple-input multiple-output spatial streams. Each optical signal output terminal of the optical demultiplexing module is connected to the corresponding optical signal input terminal of each photodetector in the photodetector module. The signal output terminals of each photodetector are independently connected to the respective signal input terminals of the adaptive analog calibration network. The adaptive analog calibration network and subsequent processing modules all employ a purely analog hardware architecture and do not incorporate an analog-to-digital converter.

[0013] Preferably, the electronically controlled variable attenuator is an electronically controlled PIN diode variable attenuator, employing a π-type attenuator topology or a T-type attenuator topology. The peripheral circuit of the electronically controlled PIN diode variable attenuator consists of a combination of series PIN diodes, parallel PIN diodes, and an RF choke. A DC control voltage is injected into the RF choke to conduct to each PIN diode. By interleaving the impedance states of the series and parallel PIN diodes, the signal transmission amplitude of the corresponding RF channel is adjusted.

[0014] Preferably, the electronically controlled variable phase shifter is an electronically controlled PIN diode variable phase shifter, employing a reflective phase shifter structure, including a 3dB quadrature coupler and two symmetrically arranged reflective loads. The reflective loads are composed of PIN diodes and microstrip branches. A DC control voltage is synchronously injected into the voltage control terminals of the PIN diodes within the two reflective loads, changing the impedance parameters of the PIN diodes and causing a change in the phase of the reflection coefficient of the reflective loads, thereby adjusting the phase of the analog radio frequency signal.

[0015] Preferably, the pilot feedback control loop includes a pilot separation and bandpass filter extraction network, and an error extraction and voltage conversion circuit. The pilot separation and bandpass filter extraction network comprises a microstrip sampling coupler and a high-Q ceramic dielectric bandpass filter, utilizing band selectivity to filter out wireless communication RF data signals and separate the reference pilot signal component. The error extraction and voltage conversion circuit includes a dual-channel RF logarithmic detector and an analog phase detector. The dual-channel RF logarithmic detector compares the amplitude differences of the reference pilot signal components in each channel and outputs a first DC voltage representing the pilot amplitude difference. The analog phase detector compares the phase differences of the reference pilot signal components in each channel and outputs a second DC voltage representing the inter-channel phase offset.

[0016] Preferably, the pilot feedback control loop further includes a first proportional-integral (PI) regulator and a second PI regulator constructed from operational amplifier hardware circuitry. The first PI regulator receives a first DC voltage, and its internal operational control equations perform proportional amplification and time integration operations on the first DC voltage to generate an attenuation control voltage. The first PI regulator utilizes its proportional gain constant and integral gain constant to complete the proportional amplification and time integration operations. The attenuation control voltage is injected as a DC control voltage into the electronically controlled variable attenuator.

[0017] Preferably, the second proportional-integral (PI) regulator receives a second DC voltage. The internal control equations of the second PI regulator perform proportional amplification and time integration operations on the second DC voltage to generate a phase-shifting control voltage. The second PI regulator utilizes its proportional gain constant and integral gain constant to complete the proportional amplification and time integration operations. The phase-shifting control voltage is injected as a DC control voltage into the electronically controlled variable phase shifter.

[0018] A second aspect of this invention provides a method for analog optical-over-wireless MIMO transmission based on pilot adaptive calibration, applied to the aforementioned analog optical-over-wireless MIMO transmission system based on pilot adaptive calibration, comprising the following: S1. The near-end access unit identifies the number of spatial streams in the multiple-input multiple-output system and generates a number of reference pilot signals corresponding to the number of spatial streams. The frequencies of each reference pilot signal do not overlap and are set within the guard band of the operating frequency band. The near-end access unit combines each reference pilot signal with the corresponding analog radio frequency signal to form a multi-channel composite transmission signal. S2, the near-end access unit uses a dense wavelength division multiplexing transmission module to input the multiple composite transmission signals formed in S1 into a single optical fiber for parallel transmission, and restores them to analog radio frequency electrical signals in the far-end unit. S3. The remote unit filters out the reference pilot signal components from the analog radio frequency electrical signal restored in S2 through a bandpass filter at the antenna front end. The remote unit configures the first reference pilot signal component as the reference reference channel, compares the amplitude difference between the other channels and the reference reference channel through a dual-channel radio frequency logarithmic detector to extract the amplitude error introduced by the optical link, and compares the phase difference between the other channels and the reference reference channel through an analog phase detector to extract the phase error introduced by the optical link. S4. The remote unit converts the amplitude error and phase error extracted in S3 into a DC control voltage. The DC control voltage is used to reverse-adjust the electronically controlled variable attenuator and electronically controlled variable phase shifter in the front stage. The imbalance between channels is eliminated through a pure analog hardware negative feedback mechanism.

[0019] This invention provides an analog optical wireless MIMO transmission system and method based on pilot adaptive calibration. It has the following beneficial effects: 1. This invention injects non-overlapping reference pilot signals into the out-of-band guard band of analog radio frequency signals and uses a dense wavelength division multiplexing (DWDM) module to transmit multiple composite transmission signals in parallel on a single optical fiber. This provides the same physical propagation path for multiple channels of signals, overcomes the optical path difference problem caused by length differences when multiple optical fibers transmit independently, avoids phase jitter of spatial stream signals during optical transmission, and achieves consistency of the physical transmission environment of the multi-input multi-output system and accurate extraction of the reference pilot signal.

[0020] 2. This invention constructs a pilot feedback control loop using a pure analog hardware architecture at the remote end, uses a filter to separate the reference pilot signal, configures a logarithmic detector and a phase detector to compare the amplitude and phase differences between channels, and generates a DC control voltage through hardware calculation via a proportional-integral regulator. The overall signal flow process does not rely on the intervention of an analog-to-digital converter or microcontroller, thus avoiding the processing delay caused by digital calculation from the physical circuit, realizing the rapid extraction of channel transmission errors and the real-time output of closed-loop drive signals.

[0021] 3. This invention connects an electronically controlled variable attenuator and an electronically controlled variable phase shifter in series in each RF channel of the adaptive analog calibration network, receives the DC control voltage output from the feedback control loop, and directly adjusts the signal amplitude and phase of each channel in the analog domain by using the characteristic of the DC control voltage to change the diode impedance. This dynamically eliminates the amplitude and phase differences between spatial flows, cancels the physical imbalance added by the fiber optic transmission link, and realizes the precise alignment of multi-channel RF signals and the hardware adaptive calibration of the antenna front-end. Attached Figure Description

[0022] Figure 1 This is a diagram of the overall system architecture of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] See attached document Figure 1 This invention provides an analog optical wireless MIMO transmission system based on pilot adaptive calibration, comprising: a near-end access unit, a single-mode fiber optic transmission link, and a far-end unit.

[0025] The near-end access unit is connected to the far-end unit via a single-mode fiber optic transmission link. The near-end access unit includes a MIMO (Multiple-Input Multiple-Output) RF input module, a pilot injection module, and a DWDM (Dense Wavelength Division Multiplexing) transmission module. The MIMO RF input module receives multiple independent analog RF signals. The output of the MIMO RF input module is connected to the input of the pilot injection module. The pilot injection module injects reference pilot signals into the out-of-band frequency band of each analog RF signal. Each reference pilot signal has a specific frequency and initial phase, and their frequencies are staggered. The output of the pilot injection module is connected to the input of the DWDM transmission module. The DWDM transmission module modulates the injected pilot signals onto lasers of different wavelengths and combines them via an optical combiner into the single-mode fiber optic transmission link.

[0026] The remote unit includes an optical demultiplexing module, a photodetector, an adaptive analog calibration network, and a pilot feedback control loop. The optical demultiplexing module separates multi-wavelength analog optical signals from a single-mode fiber. The output of the optical demultiplexing module is connected to the input of the photodetector. The photodetector converts each optical signal into an analog radio frequency (RF) signal containing both RF signals and out-of-band pilot signals. The adaptive analog calibration network is connected to the output of the photodetector, and it connects an electrically controlled variable attenuator and an electrically controlled variable phase shifter in series in each RF channel.

[0027] The pilot feedback control loop extracts the sampled signal from the output of the adaptive analog calibration network and filters out the out-of-band pilot signal. The loop calculates the amplitude and phase differences of the pilot signals for each channel using an analog detector circuit and a phase comparator circuit, and outputs a DC control voltage. This DC control voltage is fed back to the adaptive analog calibration network and input to the voltage control terminals of the electronically controlled variable attenuator and the electronically controlled variable phase shifter, respectively.

[0028] This invention provides a method for analog optical wireless MIMO transmission based on pilot adaptive calibration, comprising the following: The near-end access unit identifies the number of streams in the multiple-input multiple-output system and generates a corresponding number of reference pilot signals. The frequencies of each reference pilot signal do not overlap and are set within the guard band of the operating frequency band. The near-end access unit then merges each reference pilot signal with its corresponding analog radio frequency signal.

[0029] The near-end access unit uses a dense wavelength division multiplexing module to input the combined signals into a single optical fiber for parallel transmission.

[0030] The remote unit filters out each reference pilot signal at the antenna front end using an analog filter. The remote unit measures the amplitude of the reference pilot signal using an RF logarithmic detector and compares the phase of the reference pilot signal with that of the reference channel pilot signal using an analog phase detector. The remote unit extracts the amplitude and phase errors introduced by the optical link.

[0031] The remote unit converts amplitude and phase errors into DC control voltage. This DC control voltage drives the hardware phase shifter and attenuator in the antenna preamplifier stage. The remote unit eliminates inter-channel imbalance through a negative feedback mechanism.

[0032] The specific internal hardware structure of analog filters, envelope detectors, analog phase detectors, and optical communication devices is known to those skilled in the art and is considered common technology in the field, so it will not be described in detail here.

[0033] The present invention provides a near-end access unit, comprising: a multiple-input multiple-output radio frequency input module and a pilot injection module.

[0034] The MIMO (Multiple-Input Multiple-Output) RF input module is configured to receive independent analog RF signals. The signal receiver of the MIMO RF input module connects to a wireless access point and receives N×N independent analog RF signals from the access point. The number of spatial streams N supported by the MIMO RF input module is set to 2 or 4, corresponding to receiving 2×2 or 4×4 independent analog RF signals.

[0035] The MIMO (Multiple Input Multiple Output) RF input module receives multiple analog RF signals operating in the 5GHz band. The frequency range of the analog RF signals is defined as 5.15GHz to 5.85GHz.

[0036] The signal output terminal of the MIMO (Multiple-Input Multiple-Output) RF input module is connected to the signal input terminal of the pilot injection module. The pilot injection module injects a reference pilot signal into the downstream link of the MIMO RF input module. The center frequency band of the reference pilot signal is selected as 4.9 GHz. The 4.9 GHz band is outside the lower guard band of the 5.15 GHz to 5.85 GHz analog RF signals.

[0037] The 4.9 GHz band does not overlap with the 5.15 GHz to 5.85 GHz band, isolating the reference pilot signal from the analog radio frequency signal in the frequency domain. The 4.9 GHz reference pilot band is adjacent to the 5 GHz operating band and is used to reflect the dispersion state and transmission characteristics of the 5 GHz analog radio frequency signal during transmission through the optical fiber link.

[0038] The present invention provides a pilot injection module, comprising: a local analog oscillator and a microstrip line directional coupler.

[0039] The pilot injection module internally contains a number of local analog oscillators equal to the number of MIMO spatial streams, and a number of microstrip line directional couplers equal to the number of MIMO spatial streams. Taking a 2×2 MIMO system as an example, the pilot injection module includes two local analog oscillators and two microstrip line directional couplers. The first local analog oscillator generates a first reference pilot signal at 4.90 GHz. The second local analog oscillator generates a second reference pilot signal at 4.91 GHz. A 10 MHz frequency gap is maintained between the first and second reference pilot signals. This 10 MHz frequency gap is used to prevent spectral aliasing when the reference pilot signal is extracted at the remote end.

[0040] The reference pilot signal generated by the local analog oscillator is a continuous sinusoidal electrical signal with a constant initial amplitude and a specific center frequency.

[0041] The coupling parameters of the microstrip line directional coupler are set to -15dB to -20dB. The signal input port of the first microstrip line directional coupler is connected to the first output port of the MIMO (Multiple-Input Multiple-Output) RF input module, and the coupling port of the first microstrip line directional coupler is connected to the signal output port of the first local analog oscillator. The signal input port of the second microstrip line directional coupler is connected to the second output port of the MIMO RF input module, and the coupling port of the second microstrip line directional coupler is connected to the signal output port of the second local analog oscillator.

[0042] The microstrip line directional coupler uses a linear amplitude coefficient determined by the physical coupling degree to control the amplitude of the received reference pilot signal. The microstrip line directional coupler then directly superimposes the processed reference pilot signal onto the corresponding independent analog RF signal to form a composite transmit signal. The signal output port of the microstrip line directional coupler is connected to the signal input port of the dense wavelength division multiplexing (DWDM) transmit module, sending the composite transmit signal into the DWDM transmit module.

[0043] The present invention provides a dense wavelength division multiplexing (DWDM) transmitter module, comprising: a DWDM laser array and an optical combiner.

[0044] The dense wavelength division multiplexing (DWDM) transmitter module is specifically a DWDM colored light module. The DWDM laser array contains a number of semiconductor lasers equal to the number of spatial streams in the multiple-input multiple-output (MIMO) system. Taking an MIMO system supporting N spatial streams as an example, the DWDM laser array contains N semiconductor lasers with different center wavelengths. The electrical signal input terminal of the DWDM transmitter module is connected to the signal output terminal of the pilot injection module, receiving a composite transmit signal containing a reference pilot signal and an analog radio frequency (RF) signal. The first to Nth composite transmit signals are independently input to the RF modulation input terminals of the corresponding first to Nth semiconductor lasers.

[0045] The semiconductor laser converts the received composite emitted electrical signal into an electro-optic signal, modulating it to generate an analog optical signal of a specific wavelength. The N optical input terminals of the optical combiner are respectively connected to the optical signal output terminals of the first to the Nth semiconductor lasers.

[0046] An optical combiner multiple analog optical signals with different center wavelengths and merges them into a single converged optical signal. The optical signal output of the optical combiner is connected to the input port of a single-mode fiber optic transmission link, sending the converged optical signal into the single-mode fiber.

[0047] N-channel hybrid signals with high isolation are transmitted in parallel within a single optical fiber. This single physical fiber provides the same physical propagation path for multiple wavelength optical signals, avoiding the slight differences in physical length that occur when multiple physical fibers are used for independent transmission. This co-fiber transmission physical architecture suppresses optical path differences caused by variations in fiber length, eliminating severe phase jitter in the transmission of multi-channel, multi-input, multi-output spatial stream signals via the optical link.

[0048] This invention provides a front-end link for a remote unit, comprising: an optical demultiplexing module and a photodetector module.

[0049] The optical signal input of the optical demultiplexing module is connected to the optical signal output of the single-mode fiber transmission link. The optical demultiplexing module receives the converged optical signal transmitted in parallel through the single-mode fiber. Based on wavelength characteristics, the optical demultiplexing module separates the multi-wavelength converged optical signal in a single fiber into multiple input multiple output spatial streams (MIMOS). of Analog optical signals with independent wavelengths.

[0050] The photodetector module integrates Each is an independent photodetector. The first to second modules of the optical demultiplexing module... Each optical signal output terminal is connected to the first to the second optical detector module, respectively. The optical signal input terminal of a photodetector.

[0051] First to the Each photodetector performs a photoelectric conversion operation, converting the received first to second... The independent wavelength analog optical signals of each path are respectively restored to the first to the second. Each analog radio frequency (RF) signal output by the photodetector module synchronously includes the original wireless communication RF data signal and a reference pilot signal mixed in outside the operating frequency band guard band. The wireless communication RF data signal is specifically a Wi-Fi RF signal.

[0052] The front-end link and subsequent processing modules of the remote unit both adopt a pure analog hardware architecture. The analog radio frequency signal restored by the photodetector module flows directly in the analog domain without being connected to an analog-to-digital converter or digital baseband processing chip. (First to...) The signal output terminals of each photodetector are independently connected to the first to second adaptive analog calibration network. Each signal input terminal directly sends the analog radio frequency electrical signal to the lower-level hardware network for processing.

[0053] This invention provides an electronically controlled PIN diode variable attenuator, comprising: a series PIN diode, a parallel PIN diode, and an RF choke.

[0054] An electronically controlled PIN diode variable attenuator is configured in series in each RF channel of the adaptive analog calibration network. Taking a π-type attenuator topology as an example, the series PIN diode is connected between the RF signal input and RF signal output of the electronically controlled PIN diode variable attenuator. One end of each of the two parallel PIN diodes is connected to the two ends of the series PIN diode, and the other ends of the two parallel PIN diodes are grounded together. The RF signal input of the electronically controlled PIN diode variable attenuator is connected to the RF signal output of the photodetector module.

[0055] One end of the RF choke connects to the junction of the series and parallel PIN diodes, while the other end connects to the voltage control terminal. The RF choke is used to conduct the DC control voltage while simultaneously preventing analog RF signals from leaking to the voltage control terminal.

[0056] PIN diodes exhibit purely resistive characteristics in the radio frequency band. The remote pilot feedback control loop outputs a DC control voltage. DC control voltage Connect to the voltage control terminal of the electronically controlled PIN diode variable attenuator.

[0057] DC control voltage Increasing the forward current injected into the PIN diode leads to an increase in the forward current. This increased forward current reduces the equivalent RF impedance of the PIN diode. The electronically controlled PIN diode variable attenuator adjusts the signal transmission amplitude of the corresponding RF channel by interleaving the impedance states of the series and parallel PIN diodes.

[0058] The electrically controlled PIN diode variable attenuator performs highly linear and phase-shift-free amplitude attenuation for analog RF signals in the 4.9 GHz to 5.8 GHz frequency band. The amplitude attenuation dynamic range provided by the electrically controlled PIN diode variable attenuator is defined as 0 dB to 25 dB. The electrically controlled PIN diode variable attenuator utilizes a purely analog hardware structure to compensate for inter-channel amplitude imbalances caused by optical path transmission.

[0059] The present invention provides an electronically controlled PIN diode variable phase shifter, comprising: a 3dB quadrature coupler and two symmetrically arranged reflective loads.

[0060] An electrically controlled PIN diode variable phase shifter and an electrically controlled PIN diode variable attenuator are configured in series in the adaptive analog calibration network. The electrically controlled PIN diode variable phase shifter adopts a reflective phase shifter structure. The 3dBquadrature coupler is specifically a 90° hybrid network. The 3dBquadrature coupler has an input port, a through port, a coupling port, and an isolation port. The input port of the 3dBquadrature coupler is connected to the RF signal output terminal of the electrically controlled PIN diode variable attenuator to receive the analog RF signal. The through port of the 3dBquadrature coupler is connected to the first reflective load. The coupling port of the 3dBquadrature coupler is connected to the second reflective load. The isolation port of the 3dBquadrature coupler outputs the phase-shifted analog RF signal.

[0061] The first and second reflective loads are completely symmetrical in physical circuitry. Both the first and second reflective loads are composed of PIN diodes and microstrip branches. The microstrip branches are specifically configured as either short-circuited or open-circuited microstrip branches. The PIN diodes and microstrip branches are connected in series or in parallel.

[0062] Pilot feedback control loop calculates and generates DC control voltage Both the PIN diodes in the first and second reflective loads have voltage control terminals. DC control voltage. The voltage control terminals of the PIN diodes in the first and second reflective loads are synchronously injected, changing the impedance parameters of the PIN diodes. This change in PIN diode impedance causes a phase shift in the reflection coefficients of the first and second reflective loads.

[0063] After being reflected by the first and second reflective loads, the analog RF signal returns to the 3dB quadrature coupler and is superimposed at the isolation port. After superposition at the isolation port, the phase of the analog RF signal is continuously adjusted.

[0064] Operating in the 4.9 GHz to 5.8 GHz frequency band, the electronically controlled PIN diode variable phase shifter achieves continuous linear phase shifts from 0° to 180° or from 0° to 360°. The electronically controlled PIN diode variable phase shifter provides phase compensation parameters to precisely align phase deviations in multiplexed input multiple output channels caused by optical path differences.

[0065] This invention provides a pilot separation and bandpass filter extraction network, comprising: a microstrip sampling coupler and a bandpass filter.

[0066] Pilot separation and bandpass filter extraction networks contain a number of elements equal to the number of multi-input multi-output spatial streams. Microstrip sampling coupler and bandpass filter. First to... The inputs of each microstrip sampling coupler are independently connected to the first to second adaptive analog calibration network. One radio frequency signal output terminal. First to... The main output terminals of each microstrip sampling coupler are independently connected to the first to the second... Root radio frequency antenna. First to second The coupling output terminals of each microstrip sampling coupler are respectively connected to the first to the second... The signal input terminal of a bandpass filter.

[0067] First to the A microstrip sampling coupler shuns a portion of the analog radio frequency signal before antenna radiation as a sampling signal, which is then fed into a purely analog closed-loop feedback circuit. The shunting coupling parameter of the microstrip sampling coupler is set to -20dB.

[0068] First to the A bandpass filter receives the sampled signal output from the microstrip sampling coupler. Specifically, the bandpass filter is a high-Q ceramic dielectric bandpass filter. The circuit topology of the bandpass filter is configured as either a pure analog RC filter or a pure analog LC filter. The center frequency of the ceramic dielectric bandpass filter is configured to be 4.9 GHz, and the bandwidth is configured to be 20 MHz.

[0069] The sampling signal of the input bandpass filter includes wireless communication data signals in the 5.15 GHz to 5.85 GHz frequency band and reference pilot signals operating in the 4.90 GHz and 4.91 GHz frequency bands. The bandpass filter filters out the data signals in the 5.15 GHz to 5.85 GHz frequency band and separates the reference pilot signal components in the 4.90 GHz and 4.91 GHz frequency bands.

[0070] First to the The signal outputs of each bandpass filter are connected to the signal inputs of the subsequent error extraction and voltage conversion circuits. The bandpass filters then transmit the extracted multi-channel reference pilot signals to the dual-channel RF logarithmic detector and the analog phase detector.

[0071] The present invention provides an error extraction and voltage conversion circuit, comprising: a dual-channel radio frequency logarithmic detector and an analog phase detector.

[0072] The error extraction and voltage conversion circuit is connected to the signal output of the preceding bandpass filter. Taking a multi-input multi-output system containing two spatial streams as an example, the signal output of the first bandpass filter is connected to the first RF input of the dual-channel RF logarithmic detector and the first signal input of the analog phase detector, respectively. The signal output of the second bandpass filter is connected to the second RF input of the dual-channel RF logarithmic detector and the second signal input of the analog phase detector, respectively.

[0073] The first bandpass filter outputs a first reference pilot signal component with a center frequency of 4.90 GHz. The second bandpass filter outputs a second reference pilot signal component with a center frequency of 4.91 GHz. A dual-channel RF logarithmic detector synchronously receives both the first and second reference pilot signal components.

[0074] The error extraction and voltage conversion circuit configures the first reference pilot signal component as the reference reference channel. The dual-channel RF logarithmic detector specifically uses a pure analog chip with an AD8302 architecture. The dual-channel RF logarithmic detector uses the first reference pilot signal component as the amplitude reference and compares the amplitude difference between the first and second reference pilot signal components. The dual-channel RF logarithmic detector converts the amplitude difference into a first DC voltage and outputs it. The first DC voltage represents the amplitude difference between the two pilot signals. .

[0075] The analog phase detector synchronously receives the first and second reference pilot signal components. Using the first reference pilot signal component as a phase reference, the analog phase detector measures the phase offset of the second reference pilot signal component relative to the first reference pilot signal component. The analog phase detector converts the phase offset into a second DC voltage and outputs it. This second DC voltage represents the phase bias between channels. .

[0076] The voltage output terminals of the dual-channel RF logarithmic detector and the analog phase detector are connected to the signal input terminals of the subsequent proportional-integral (PI) regulator. The first DC voltage output from the dual-channel RF logarithmic detector and the second DC voltage output from the analog phase detector are fed into the PI regulator.

[0077] The present invention provides a proportional-integral regulator and a negative feedback drive circuit, comprising: a first proportional-integral regulator and a second proportional-integral regulator.

[0078] Taking a multi-input multi-output system including a first spatial flow reference channel and a second spatial flow compensation channel as an example, the signal input terminal of the first proportional-integral (PI) regulator is connected to the voltage output terminal of a dual-channel RF logarithmic detector. The first PI regulator receives a first DC voltage representing the pilot amplitude difference. The signal input of the second proportional-integral (PI) regulator is connected to the voltage output of the analog phase detector. The second PI regulator receives a second DC voltage representing the inter-channel phase bias. .

[0079] Both the first and second proportional-integral (PI) regulators are constructed using operational amplifier hardware circuitry. The first PI regulator configures its proportional and integral gains through the resistor-capacitor network of the operational amplifier. The first PI regulator operates on a first DC voltage... Perform proportional amplification and time integration operations to generate attenuation control voltage. The operational control equation configured inside the first proportional-integral controller is as follows:

[0080] in, This represents the proportional gain constant of the first proportional-integral controller. This represents the integral gain constant of the first proportional-integral controller. This represents the time integral variable.

[0081] The second proportional-integral (PI) regulator configures the proportional gain and integral gain through the resistor-capacitor network of the operational amplifier. The second PI regulator is configured to operate on the second DC voltage. Perform proportional amplification and time integration operations to generate phase-shift control voltage. The operational control equation configured inside the second proportional-integral controller is as follows:

[0082] in, This represents the proportional gain constant of the second proportional-integral controller. This represents the integral gain constant of the second proportional-integral controller.

[0083] The voltage output of the first proportional-integral (PI) regulator is connected to the voltage control terminal of the electronically controlled PIN diode variable attenuator in the second space current compensation channel of the pre-amplifier adaptive analog calibration network. The first PI regulator attenuates the control voltage. The voltage is injected into the electronically controlled PIN diode variable attenuator. The voltage output of the second proportional-integral regulator is connected to the voltage control terminal of the electronically controlled PIN diode variable phase shifter in the second space current compensation channel of the preceding adaptive analog calibration network. The second proportional-integral regulator controls the phase shift voltage. Injected into an electronically controlled PIN diode variable phase shifter.

[0084] A proportional-integral regulator, an adaptive analog calibration network, and an error extraction and voltage conversion circuit together constitute a negative feedback hardware control closed loop. The negative feedback hardware control closed loop utilizes voltage attenuation. With phase shift control voltage The amplitude and phase parameters of the reverse adjustment compensation channel.

[0085] The negative feedback hardware control closed loop continuously executes dynamic adjustment operations, forcing the first DC voltage... With the second DC voltage Convergence approaches zero, eliminating the imbalance between the compensation channel and the reference channel. The error convergence process of the negative feedback hardware control closed loop does not rely on microcontroller calculations; it is implemented entirely through a pure analog hardware loop. The convergence response time of the pure analog hardware loop is in the microsecond range.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pilot-adaptive calibration-based analog optical wireless MIMO transmission system, comprising a near-end access unit, a single-mode fiber optic transmission link, and a far-end unit, wherein the near-end access unit is connected to the far-end unit via the single-mode fiber optic transmission link, characterized in that, The near-end access unit includes a multiple-input multiple-output (MIMO) RF input module, a pilot injection module, and a dense wavelength division multiplexing (DWDM) transmission module. The output of the MIMO RF input module is connected to the input of the pilot injection module. The pilot injection module injects a reference pilot signal into the out-of-band frequency band of each analog RF signal. The output of the pilot injection module is connected to the input of the DWDM transmission module. The DWDM transmission module controls semiconductor lasers of different wavelengths to convert the multiple analog signals after the injection of the reference pilot signal into optical signals, and combines them into the single-mode fiber optic transmission link via an optical combiner. The remote unit includes an optical demultiplexing module, a photodetector module, an adaptive analog calibration network, and a pilot feedback control loop; the output of the optical demultiplexing module is connected to the input of the photodetector module; the photodetector module converts each optical signal into an analog radio frequency electrical signal containing wireless communication radio frequency data signals and reference pilot signals; the adaptive analog calibration network is connected to the output of the photodetector module, and the adaptive analog calibration network connects an electrically controlled variable attenuator and an electrically controlled variable phase shifter in series in each radio frequency channel; The pilot feedback control loop extracts the sampling signal from the output of the adaptive analog calibration network and filters out the reference pilot signal; The pilot feedback control loop calculates the amplitude difference and phase difference of the reference pilot signals of each channel and outputs a DC control voltage; the DC control voltage is fed back to the adaptive analog calibration network and input to the voltage control terminal of the electronically controlled variable attenuator and the voltage control terminal of the electronically controlled variable phase shifter, respectively.

2. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 1, characterized in that, The pilot injection module includes a number of local analog oscillators equal to the number of multi-input multi-output space streams and microstrip line directional couplers; The signal input port of the microstrip directional coupler is connected to the output port of the multiple-input multiple-output RF input module, and the coupling port of the microstrip directional coupler is connected to the signal output port of the local analog oscillator; the microstrip directional coupler superimposes the reference pilot signals generated by each local analog oscillator onto the corresponding analog RF signal to form a composite transmission signal; the frequencies of each reference pilot signal do not overlap.

3. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 2, characterized in that, The dense wavelength division multiplexing (DWDM) transmitting module includes a DWDM laser array and an optical combiner. The dense wavelength division multiplexing laser array comprises semiconductor lasers with a number equal to the number of multiple input multiple output spatial streams and different center wavelengths. Each composite emission signal is independently input to the radio frequency modulation input terminal of the corresponding semiconductor laser, and after electro-optic conversion, it is multiplexed and combined into a single converged optical signal by the optical combiner and sent into the single-mode fiber optic transmission link for parallel transmission.

4. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 1, characterized in that, The photodetector module integrates an equal number of independent photodetectors as the number of multiple input multiple output spatial streams. Each optical signal output terminal of the optical demultiplexing module is respectively connected to the optical signal input terminal of each photodetector in the photodetector module; the signal output terminal of each photodetector is independently connected to each signal input terminal of the adaptive analog calibration network; the adaptive analog calibration network and subsequent processing modules all adopt a pure analog hardware architecture and are not connected to an analog-to-digital converter.

5. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 1, characterized in that, The electronically controlled variable attenuator is an electronically controlled PIN diode variable attenuator, which adopts a π-type attenuator topology or a T-type attenuator topology. The peripheral circuit of the electronically controlled PIN diode variable attenuator is composed of a series PIN diode, a parallel PIN diode and an RF choke. The DC control voltage is injected into the RF choke coil to conduct to each PIN diode. By interleaving the impedance states of the series PIN diodes and the parallel PIN diodes, the signal transmission amplitude of the corresponding RF channel is adjusted.

6. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 1, characterized in that, The electronically controlled variable phase shifter is an electronically controlled PIN diode variable phase shifter, which adopts a reflective phase shifter structure, including a 3dB quadrature coupler and two symmetrically arranged reflective loads; The reflective load is composed of PIN diodes and microstrip sections; the DC control voltage is synchronously injected into the voltage control terminals of the PIN diodes in the two reflective loads, changing the impedance parameters of the PIN diodes and causing a change in the phase of the reflection coefficient of the reflective load, thereby adjusting the phase of the analog radio frequency signal.

7. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 1, characterized in that, The pilot feedback control loop includes a pilot separation and bandpass filter extraction network as well as an error extraction and voltage conversion circuit. The pilot separation and bandpass filter extraction network includes a microstrip sampling coupler and a high-Q ceramic dielectric bandpass filter, which uses the frequency band selection characteristics to filter out wireless communication radio frequency data signals and separate the reference pilot signal components. The error extraction and voltage conversion circuit includes a dual-channel RF logarithmic detector and an analog phase detector; the dual-channel RF logarithmic detector compares the amplitude difference of the reference pilot signal components of each channel and outputs a first DC voltage representing the pilot amplitude difference; the analog phase detector compares the phase difference of the reference pilot signal components of each channel and outputs a second DC voltage representing the phase offset between channels.

8. The analog optical wireless MIMO transmission system based on pilot adaptive calibration according to claim 7, characterized in that, The pilot feedback control loop also includes a first proportional-integral regulator and a second proportional-integral regulator, which are constructed from operational amplifier hardware circuits. The first proportional-integral regulator receives the first DC voltage. The operational control equation configured inside the first proportional-integral regulator is to perform proportional amplification and time integration operations on the first DC voltage to generate an attenuation control voltage. The first proportional-integral regulator uses the proportional gain constant and the integral gain constant of the first proportional-integral regulator to complete the proportional amplification and time integration operations. The attenuation control voltage is injected as a DC control voltage into the electronically controlled variable attenuator.

9. The analog optical-over-wireless MIMO transmission system based on pilot adaptive calibration according to claim 8, characterized in that, The second proportional-integral (PI) regulator receives the second DC voltage. The operational control equation configured inside the second PI regulator is to perform proportional amplification and time integration operations on the second DC voltage to generate a phase-shift control voltage. The second PI regulator uses its proportional gain constant and integral gain constant to complete the proportional amplification and time integration operations. The phase-shift control voltage is injected as a DC control voltage into the electronically controlled variable phase shifter.

10. A method for analog optical-over-wireless MIMO transmission based on pilot adaptive calibration, applied to the analog optical-over-wireless MIMO transmission system based on pilot adaptive calibration as described in any one of claims 1 to 9, characterized in that, include: S1. The near-end access unit identifies the number of spatial streams in the multiple input multiple output system and generates a number of reference pilot signals corresponding to the number of spatial streams. The frequencies of each of the reference pilot signals do not overlap and are set within the guard band of the operating frequency band; the near-end access unit combines each of the reference pilot signals with the corresponding analog radio frequency signal to form a multi-channel composite transmission signal; S2. The near-end access unit uses a dense wavelength division multiplexing transmission module to input the multi-channel composite transmission signal formed in S1 into a single optical fiber for parallel transmission, and restores it to an analog radio frequency electrical signal in the far-end unit. S3. The remote unit filters out each reference pilot signal component from the analog radio frequency electrical signal restored in S2 through a bandpass filter at the antenna front end; the remote unit configures the first reference pilot signal component as a reference reference channel, compares the amplitude difference between the other channels and the reference reference channel through a dual-channel radio frequency logarithmic detector to extract the amplitude error introduced by the optical link, and compares the phase difference between the other channels and the reference reference channel through an analog phase detector to extract the phase error introduced by the optical link; S4. The remote unit converts the amplitude error and phase error extracted in S3 into a DC control voltage; it uses the DC control voltage to reverse adjust the electronically controlled variable attenuator and electronically controlled variable phase shifter of the preceding stage, and eliminates the imbalance between channels through a pure analog hardware negative feedback mechanism.

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