CN107040311B - Bidirectional photon radio frequency transmission system for self-homodyne coherent detection and signal processing implementation method thereof - Google Patents
Bidirectional photon radio frequency transmission system for self-homodyne coherent detection and signal processing implementation method thereof Download PDFInfo
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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Abstract
The invention discloses a bidirectional photon radio frequency transmission system for self homodyne coherent detection and a signal processing implementation method thereof, wherein the transmission system comprises a CW laser, a downlink and an uplink, and a high-frequency orthogonal MQAM-OFDM transmitter is mainly adopted in the downlink and the uplink to realize the processing of key signals.
Description
[ technical field ]
The invention relates to the technical field of new generation information and communication, in particular to a self-homodyne coherent detection two-way photon radio frequency transmission system and a signal processing implementation method thereof.
Background art
With the rapid development of Information Communication Technology (ICT), efforts and attempts are continually being made to pursue ultra-large bandwidth, ultra-long range transmissions. The coherent photon communication can realize ultra-high-speed signal transmission, and the coherent detection can improve the sensitivity of the receiver, and under the same optical communication condition, the coherent receiver improves the sensitivity by about 20dB compared with a common receiver, and can achieve high performance close to the limit of shot noise, so that the unrepeatered transmission distance of the optical signal is also increased. The signal reception of the coherent photon communication is divided into heterodyne detection reception and homodyne detection reception, and the homodyne detection has higher receiving sensitivity. With the increasing demands of people for ultra-high-speed photon communication, the superiority of coherent optical communication based on homodyne detection is more and more highlighted.
Chinese patent 201510903299.6 discloses a polarization independent self-coherent ofdm optical fiber transmission system and transmission method, which includes a transmitting end and a receiving end, wherein the transmitting end generates an ofdm signal by means of quadrature modulation. For the OFDM signal, the frequency spectrum around the zero frequency is vacated for transmitting the carrier wave; the receiving end separates the carrier wave and the signal by a filter, and the carrier wave is changed into circularly polarized light by a 1/4 wave plate; and finally, inputting the carrier wave and the signal into a coherent receiver and carrying out subsequent digital signal processing.
The scheme has the following problems in design and implementation:
(1) According to the expression in the chinese patent 201510903299.6, one path of laser light wave which is separated by the optical coupler 1 and is not modulated is coupled with another path of modulated laser carrier signal by optical coupling to 2 paths of optical coupling, and then enters into a single-mode fiber to be transmitted to a receiving end.
However, we can learn from the 1/4 wave plate optical processing principle: the laser light wave which is not modulated is sourced from the laser 1, is not polarized and is not linearly polarized; the modulated laser carrier is linearly polarized after polarization treatment; after two paths of light waves are mixed by the coupler 2, the light waves have linear polarized light and circular polarized light, and the laser tube light waves with two polarization states are processed by the receiving end through the circulator, the semi-transparent semi-reflective fiber grating and the 1/4 wave plate, so that the linear polarized light is changed into circular polarized light, and the circular polarized light is changed into linear polarized light.
The system described in chinese patent 201510903299.6 is obviously problematic in that "the laser light wave having both linearly polarized light and circularly polarized light is changed into circularly polarized light by the 1/4 wave plate", and further "polarization independent reception" disclosed in the patent is also problematic.
(2) The "spectral spacing is left near the optical carrier" disclosed in chinese patent 201510903299.6, and the "signal of the subcarrier is set to 0 near the low frequency band (-5 GHz to 5 GHz)" is problematic.
The method comprises the following steps: the implementation difficulty is relatively large, so that the implementation is impossible.
In OFDM multi-carrier modulation, its carrier frequency is relatively low, typically measured in KHz or MHz, and the number of carriers is relatively large. According to the state 201510903299.6, if the subcarrier signal in the bandwidth from-5 GHz to 5GHz is set to 0, in the current OFDM modulation, if such a large bandwidth is used for the subcarrier setting of 0, no more bandwidth OFDM signal code modulation is transmitted.
And two,: no specific embodiment is given.
In the OFDM code modulation principle, subcarrier modulation refers to modulating useful information onto a plurality of low-frequency carriers corresponding to the useful information through serial-parallel conversion, and further realizing efficient spectrum bandwidth utilization by utilizing spectrum overlapping characteristics. Whereas, in chinese patent 201510903299.6, only "set the signal of the subcarrier to 0" is described, a method of how to set the subcarrier signal to 0 is not given.
(3) According to Chinese patent 201510903299.6: the semi-transparent and semi-reflective fiber grating reflects light which does not carry useful information back and passes through the fiber grating.
Such a design is problematic: the reflected laser light wave is a central sideband light wave with a central frequency of THz bandwidth, and the modulated optical double sideband (positive and negative first order sideband) signal passes through the fiber grating. The spectral signal without the center sideband enters a polarization multiplexing coherent receiver to be demodulated with the reflected center sideband light wave, which is not called coherent detection, and the design is not realized, and is contrary to the coherent optical detection demodulation principle.
Summary of the invention
The invention aims to provide a self-homodyne coherent detection two-way photon radio frequency transmission system and a signal processing implementation method thereof, which provide a high-efficiency solution for future ultra-high speed coherent optical communication, photon radio frequency fusion communication, ultra-high speed multi-channel MIMO wireless transmission and high-speed photon radio frequency interconnection and intercommunication among base stations. The aim of the invention is realized by the following technical scheme:
a two-way photon radio frequency transmission system for self-homodyne coherent detection, comprising: CW laser, downlink and uplink; wherein, the liquid crystal display device comprises a liquid crystal display device,
the downlink includes: the input end of the first optical polarization beam splitter is connected with the output end of the CW laser, and the two output ends are respectively connected with the input ends of the MZM-1 and the MZM-2; the high-frequency orthogonal MQAM-OFDM downlink transmitter generates two pairs of I/Q signals and outputs the signals to modulation ends of MZM-1 and MZM-2 respectively; the output end of the MZM-1 is connected with one input end of the first optical polarization beam combiner; the output end of the MZM-2 is connected with the input end of the first 90-degree optical phase shifter; the output end of the first 90-degree optical phase shifter is connected with the other input end of the first optical polarization beam combiner; the optical wave signal A output by the output end of the first optical polarization beam combiner is connected to the input end of the EDFA; the output end of the EDFA is connected with the input end of the ultra-narrow band beam splitter through the first SSMF; an ultra-narrow band beam splitter, one output end outputs a light wave signal B and is connected to the input end of the optical attenuator, and the other output end outputs a light wave signal C and is connected to the input end of the 1:1:1 optical power divider; the output end of the optical attenuator is connected with one input end of the optical combiner; the first output end of the 1:1:1 optical power divider is connected with the other input end of the optical combiner, and the second output end and the third output end of the 1/4 dual-channel wave plate device are connected with the two input ends of the 1/4 dual-channel wave plate device; the optical combiner outputs an optical wave signal D at the output end and is connected to one input end of the downlink polarization multiplexing 90-degree optical mixer; a 1/4 double-channel wave plate device, wherein one output end outputs a light wave signal E and is connected to the other input end of the downlink polarization multiplexing 90-degree optical mixer; the output end of the downlink polarization multiplexing 90-degree optical mixer is connected with the input end of the downlink diversity photoelectric detector; the output end of the downlink diversity photoelectric detector is connected with the input end of the downlink high-frequency orthogonal demodulator; the output end of the downlink high-frequency orthogonal demodulator is connected with the input end of the downlink high-speed digital signal processing module; the output end of the downlink high-speed digital signal processing module outputs a downlink high-frequency digital baseband signal;
the uplink includes: the input end of the second optical polarization beam splitter is connected with the optical wave signal F output by the other output end of the 1/4 double-channel wave plate device, and the two output ends are respectively connected with the input ends of the MZM-3 and the MZM-4; the high-frequency orthogonal MQAM-OFDM downlink transmitter generates two pairs of I/Q signals and outputs the signals to modulation ends of MZM-3 and MZM-4 respectively; the output end of the MZM-3 outputs a light wave signal G and is connected with one input end of the second optical polarization beam combiner; the output end of the MZM-4 is connected with the other input end of the second optical polarization beam combiner after passing through the second 90-degree optical phase shifter; the output end of the second optical polarization beam combiner is connected with one input end of the uplink polarization multiplexing 90-degree optical mixer through a second SSMF; the other input end of the uplink polarization multiplexing 90-degree optical mixer is connected with the output of the CW laser, and the output end of the uplink polarization multiplexing 90-degree optical mixer is connected with an uplink diversity photoelectric detector; an output end of the uplink diversity photoelectric detector is connected with an uplink high-frequency orthogonal demodulator; the output end of the high-frequency orthogonal demodulator is connected with the uplink high-speed digital signal processing module; and the high-speed digital signal processing module outputs an uplink high-speed digital baseband signal.
As a specific technical scheme, the high-frequency orthogonal MQAM-OFDM downlink transmitter and the high-frequency orthogonal MQAM-OFDM downlink transmitter both adopt the following structures, and the method comprises the following steps: the input end of the ultra-high speed serial-parallel conversion output device is connected with a high-speed digital baseband signal, and the two output ends are respectively connected with the input end of the first pair of I/Q signal generating circuits and the input end of the second pair of I/Q signal generating circuits; the first pair of I/Q signal generating circuits comprises an MQAM sequence coding processing module, an OFDM modulation processing module, a double-path low-pass cut-off filtering processing module, a space-time encoder, a high-frequency quadrature amplitude modulator and an asymmetric electric signal processing module which are sequentially connected, wherein the asymmetric electric signal processing module outputs a first pair of I/Q signals; a second pair of I/Q signal generating circuits having the same circuit configuration as the first pair of I/Q signal generating circuits, and outputting a second pair of I/Q signals; the ultra-high frequency local oscillation source is characterized in that two output ends are respectively connected with modulation ends of high-frequency quadrature amplitude modulators in a first pair of I/Q signal generating circuits and a second pair of I/Q signal generating circuits, and space-time encoders in the first pair of I/Q signal generating circuits and the second pair of I/Q signal generating circuits are mutually connected.
As a specific technical scheme, the transmission system further comprises a 4x4MIMO wireless transmitter connected to the output end of the downlink diversity photoelectric detector or the output end of the uplink diversity photoelectric detector, wherein the 4x4MIMO wireless transmitter comprises four groups of wireless transmitting circuits, and each group of wireless transmitting circuits comprises an out-of-band spurious suppression filter, a radio frequency power amplifier and an antenna which are sequentially connected.
As a specific technical scheme, the transmission system further comprises a 4x4MIMO wireless receiver matched with the 4x4MIMO wireless transmitter, wherein the 4x4MIMO wireless receiver comprises four antennas which are respectively connected with four input ends of the dual-channel out-of-band spurious suppression filter; the two output ends of the two-channel out-of-band spurious suppression filter are respectively connected with the first path of decoding circuit and the second path of decoding circuit; the first path of decoding circuit comprises a high-frequency quadrature amplitude demodulator, a space-time decoder, an OFDM demodulation processing module and an MQAM sequence decoding processing module which are sequentially connected; the second path of decoding circuit, the circuit structure is the same as the first path of decoding circuit; the two output ends of the ultrahigh frequency local oscillation source are respectively connected with the modulation ends of the high frequency quadrature amplitude demodulator in the first path of decoding circuit and the second path of decoding circuit; the ultra-high speed parallel-serial conversion output device is characterized in that two input ends are respectively connected with the output end of one path of decoding circuit and the output end of a second path of decoding circuit, and the output end outputs a high-speed digital baseband signal; the space-time encoders in the first path decoding circuit and the second path decoding circuit are connected to each other.
A signal processing implementation method of a self-homodyne coherent detection two-way photon radio frequency transmission system comprises the following steps:
the laser light wave output by the CW laser is divided into two parts, one part is used for modulating downlink optical carrier signals, and the other part is used for detecting and receiving local oscillation laser signals used for uplink coherent optical signals; wherein, the liquid crystal display device comprises a liquid crystal display device,
the signal processing method of the downlink is as follows:
(1) The laser wave used for modulating the downlink optical carrier signal is subjected to laser wave linear polarization processing through a first polarization beam splitter, and then is modulated by two pairs of I/Q signals output by a high-frequency orthogonal MQAM-OFDM downlink transmitter through MZM-1 and MZM-2 respectively; (2) The modulated optical carrier signal is processed by 90-degree phase shift and then is combined with the other modulated optical carrier signal through a first polarization beam combiner, then signal amplification is carried out through an EDFA, and then the modulated optical carrier signal is transmitted to an ultra-narrow band beam splitter through a first SSMF; (3) The modulated optical carrier signal is separated into a positive and negative first-order spectrum sideband light wave signal B and a center spectrum sideband light wave signal C with the center frequency of 193.10THz and the bandwidth of 125MHz by a 1pm bandwidth ultra-narrow band beam splitter; (4) The positive and negative first-order spectrum sideband light wave signals B are input into an optical combiner after passing through an optical attenuator, the center spectrum sideband light wave signals C are divided into three paths through a 1:1:1 optical power divider, one path of signals is input into the optical combiner, and the other two paths of signals are input into a 1/4 double-channel wave plate device; (5) The optical wave signal D output by the optical combiner and the optical wave signal E of pure circularly polarized laser with the center frequency of 193.10THz output by the 1/4 double-channel wave plate device are input to a downlink polarization multiplexing 90-degree optical mixer, and four paths of output of the downlink polarization multiplexing 90-degree optical mixer are input to a downlink diversity photoelectric detector; (6) The four paths of output sequences of the downlink diversity photoelectric detector are processed by a downlink high-frequency orthogonal demodulator and a downlink high-speed digital signal processing module, and then a downlink high-speed digital baseband signal is demodulated;
the uplink signal processing method is as follows:
A. the other path of optical wave signal F of the pure circular polarized laser with the center frequency of 193.10THz output by the 1/4 double-channel wave plate device is subjected to laser optical wave linear polarization treatment through a second polarization beam splitter, and then is modulated by two pairs of I/Q signals output by a high-frequency orthogonal MQAM-OFDM uplink transmitter through MZM-3 and MZM-4 respectively; B. the modulated optical carrier signal is combined with the other modulated optical carrier signal through a second polarization beam combiner after being subjected to 90-degree phase shift treatment, and then the modulated optical carrier signal is transmitted to an uplink polarization multiplexing 90-degree optical mixer through a second SSMF; C. local oscillation laser used for implementing self-coherent detection and receiving by the uplink polarization multiplexing 90-degree optical mixer is output by a CW laser, and the uplink polarization multiplexing 90-degree optical mixer inputs two pairs of four-way photon radio frequency I/Q signals to an uplink diversity photoelectric detector to realize photoelectric detection conversion treatment; D. four paths of output sequences of the uplink polarization multiplexing 90-degree optical mixer are processed by an uplink diversity photoelectric detector, an uplink high-frequency orthogonal demodulator and an uplink high-speed digital signal processing module to demodulate an uplink high-speed digital baseband signal.
As a specific technical scheme, the process of generating two pairs of I/Q signals by the high-frequency orthogonal MQAM-OFDM downlink transmitter and the high-frequency orthogonal MQAM-OFDM uplink transmitter respectively is as follows: the accessed high-speed digital baseband signals are subjected to serial-parallel conversion through an ultra-high-speed serial-parallel conversion output device, and two paths of signals are output to a first pair of I/Q signal generating circuits and a second pair of I/Q signal generating circuits; the first pair of I/Q signal generating circuits sequentially perform MQAM sequence coding, OFDM modulation, double-path low-pass cut-off filtering module, space-time coding, high-frequency quadrature amplitude modulation and asymmetric electric signal processing on input signals and output first pair of I/Q signals; the processing procedure of the second pair of I/Q signal generating circuits is the same as that of the first pair of I/Q signal generating circuits, and the second pair of I/Q signals are output; the ultrahigh frequency local oscillation source provides oscillation sources for high frequency quadrature amplitude modulators in a first pair of I/Q signal generating circuits and a second pair of I/Q signal generating circuits, and space-time encoders in the first pair of I/Q signal generating circuits and the second pair of I/Q signal generating circuits are connected with each other.
As a specific technical scheme, in the process that the high-frequency orthogonal MQAM-OFDM downlink transmitter and the high-frequency orthogonal MQAM-OFDM uplink transmitter respectively generate two pairs of I/Q signals: before OFDM modulation, the MQAM sequence useful signal input at the front end is subjected to periodic continuous multi-zero redundancy code insertion logic coding reprocessing, so that a plurality of subcarriers at the left side and the right side of the middle frequency band in OFDM modulation are subjected to relevant zero logic operation processing in one-to-one correspondence with the continuous multi-zero redundancy codes, and due to the fact that the periodic continuous multi-zero redundancy codes are inserted, the OFDM frequency spectrum in each period can be free of 125MHz bandwidth in the middle to participate in useful signal transmission insubstantially; the high frequency carrier frequency of the high frequency quadrature amplitude modulator is 60GHz, and the frequency band can provide effective utilization bandwidth for OFDM of up to 6GHz or more.
As a specific technical solution, in the step (6) or the step D, four paths of outputs of the downlink diversity photodetector or the uplink diversity photodetector are further processed by: each output of the downlink diversity photoelectric detector or the uplink diversity photoelectric detector is subjected to out-of-band spurious suppression filtering treatment, amplified by radio frequency power and then transmitted by an antenna.
As a specific technical solution, the signal processing real-time method further includes a step of receiving a transmission signal, including: signals are received through four antennas and are respectively input to four input ends of the two-channel out-of-band spurious suppression filter; two paths of output signals of the double-channel out-of-band spurious suppression filter are processed by a first path of decoding circuit and a second path of decoding circuit respectively; the first path of decoding circuit sequentially processes the received signals by a high-frequency quadrature amplitude demodulator, a space-time decoder, an OFDM demodulation processing module and an MQAM sequence decoding processing module; the processing procedure of the second path decoding circuit to the received signal is the same as that of the first path decoding circuit; the signals processed by the first path of decoding circuit and the second path of decoding circuit are processed by an ultra-high speed parallel-serial conversion output device and then output high-speed digital baseband signals; the ultrahigh frequency local oscillation source provides an oscillation source for high frequency quadrature amplitude demodulation in the first path of decoding circuit and the second path of decoding circuit, and space-time encoders in the first path of decoding circuit and the second path of decoding circuit are connected with each other.
As a specific technical scheme, in the execution process of the step (2): the signal transmission bandwidth of the ultra-narrow band beam splitter is moderately increased, so that the local oscillator laser light wave signal bandwidth with the center frequency of 193.10THz is widened, and the relative intensity noise value is improved; the filtering bandwidth is moderately increased to improve the relative intensity noise value through the filtering function of the EDFA after the signal amplification, so that the complex-valued photocurrents I to (t) after the signal output of the diversity photodetector I, Q is combined are improved.
The invention has the beneficial effects that:
(1) The ultra-narrow band beam splitter splits the modulated optical carrier signal by using a laser light wave with a center frequency of 193.1THz and a bandwidth of 125MHz, and performs power sharing by using a 1:1:1 optical power splitter, where the split laser light wave with the center frequency of 193.1THz is a pure laser tube light wave without carrying any modulation information because of the design reason of claim 2.
(2) The laser polarization beam splitter and the polarization beam combiner are introduced in the system, the laser carrier wave in transmission is linearly polarized light, and after being processed by the 1/4 double-channel wave plate device, the laser wave with the center frequency of 193.1THz and the bandwidth of 120MHz is changed into circularly polarized light, the downlink 90-degree light mixing receiving processing has polarization independence, and the uplink laser carrier wave light source modulation also has linear polarization independence.
(3) The modulated optical carrier signal and the local oscillation laser light source input from the front end of the downlink polarization multiplexing 90-degree optical mixer are both derived from a CW laser with the center frequency of 193.1THz, and the CW laser and the local oscillation laser have the same optical path length and are synchronously locked in optical phase, so that the downlink transmission self-homodyne coherent detection and reception are realized.
(4) Four-path photon radio frequency signals carrying two pairs of I/Q information and output by the downlink diversity photoelectric detector can be directly and wirelessly transmitted through an antenna as a signal source of 4x4MIMO wireless transmission after out-of-band spurious suppression filtering and radio frequency power amplification treatment, so that the direct conversion transmission from multichannel photon radio frequency waves to wireless microwave MIMO is realized.
(5) No additional laser light source is introduced separately in the uplink laser carrier modulation process, and the laser carrier modulation transmission is implemented by means of circularly polarized light laser with linear polarization independence output by a 1/4 double-channel wave plate device in a downlink transmission system.
(6) The local oscillation laser light source used for implementing optical coherence demodulation by the uplink polarization multiplexing 90-degree optical mixer is derived from a CW laser, the central frequency of the uplink transmission laser signal carrier and the central frequency of the CW laser light source are both 193.1THz, and the uplink transmission also realizes self-homodyne optical coherence detection and reception.
(7) The local oscillation laser sources for polarization multiplexing 90-degree optical mixing detection and reception are all from a CW laser, the local oscillation laser sources are not additionally introduced, the stability and the controllability of the laser center frequency are greatly improved, and the networking and maintenance cost is remarkably reduced; and the optical fiber is universal circularly polarized light, and has linear polarization independence when photon radio frequency wave detection is received.
(8) Two pairs of four paths of I/Q signals output by the high-frequency orthogonal MQAM-OFDM transmitter respectively modulate two paths of orthogonal linear polarization laser light waves, and the modulated uplink four paths of photon radio frequency I/Q signals are transmitted to a near-end 4x4MIMO wireless transmitter to directly provide four paths of information sources corresponding to the uplink four paths of photon radio frequency I/Q signals.
(9) The high-frequency orthogonal MQAM-OFDM downlink transmitter and the high-frequency orthogonal MQAM-OFDM uplink transmitter are characterized in that the frequency of an orthogonal modulated high-frequency carrier is up-regulated to 60GHz, and a useful modulation bandwidth of more than 6GHz is implemented for a far end, so that the high-frequency orthogonal MQAM-OFDM downlink transmitter and the high-frequency orthogonal MQAM-OFDM uplink transmitter are further used for 4x4MIMO wireless carrier receiving and transmitting communication.
Description of the drawings
FIG. 1 is a schematic diagram of a two-way photon radio frequency quadrature modulation MQAM-OFDM system for self-homodyne coherent detection;
FIG. 2, a schematic diagram of a high frequency orthogonal MQAM-OFDM transmitter;
FIG. 3, an OFDM coding design in a high frequency orthogonal MQAM-OFDM transmitter, uses a schematic diagram of the spectral principle;
FIG. 4, schematic diagrams of the spectrum principle at point A in FIG. 1;
FIG. 5, schematic diagram of the spectrum principle at point B in FIG. 1;
FIG. 6, schematic diagrams of the spectrum principle at point C in FIG. 1;
FIG. 7, schematic diagram of the spectrum principle at point D in FIG. 1;
FIG. 8, schematic diagram of the spectrum principle at point E in FIG. 1;
FIG. 9, schematic diagrams of the spectral principle at point F in FIG. 1;
FIG. 10, schematic diagram of the spectral principle at point G in FIG. 1;
FIG. 11, schematic diagrams of the spectrum principle at the H point in FIG. 1;
fig. 12, 4x4MIMO wireless transmitter principle architecture diagrams;
fig. 13, 4x4MIMO wireless receiver principle architecture diagram;
fig. 14, MQAM-OFDM high frequency quadrature IQ modulation mathematical model diagram.
Best mode for carrying out the invention
The following is a further description of embodiments of the invention, taken in conjunction with the accompanying drawings:
as shown in fig. 1, the downlink signal processing and transmission process of the two-way photon radio frequency quadrature modulation MQAM-OFDM system with self-homodyne coherent detection is as follows:
the laser light wave with the central frequency of 193.10THz output by the CW laser is divided into two parts, wherein one part is used for modulating a downlink optical carrier signal, and the other part is used for detecting and receiving a local oscillation laser signal used for uplink coherent optical signal. The laser light wave used for modulating the downlink optical carrier signal is subjected to laser light wave linear polarization processing through a polarization beam splitter, then is modulated by two pairs of four paths of I/Q signals output by a high-frequency orthogonal MQAM-OFDM downlink transmitter through two photoelectric modulators (MZM-1 and MZM-2), one path of modulated optical carrier signal is subjected to 90-degree phase shift processing and then is combined with the other path of modulated optical carrier signal through a polarization beam combiner, then is subjected to signal amplification through an erbium-doped fiber amplifier (EDFA), and then is transmitted to remote equipment through a Standard Single Mode Fiber (SSMF).
The principle structure of the high-frequency orthogonal MQAM-OFDM downlink transmitter in the process is shown in figure 2. In the OFDM modulation process, the MQAM sequence useful signal input from the front end is subjected to periodic continuous multi-zero redundancy code insertion logic coding reprocessing, so that a plurality of subcarriers at the left side and the right side of the middle frequency band in the OFDM modulation are subjected to relevant zero logic operation processing in one-to-one correspondence with the continuous multi-zero redundancy codes, and due to the periodic continuous multi-zero redundancy code insertion, the OFDM frequency spectrum in each period can be free to participate in the transmission of the useful signal in an insubstantial mode, and the 125MHz bandwidth in the middle can be reserved. After insertion of the multi-zero redundancy code, the principle of OFDM spectrum is schematically shown in fig. 3. The high frequency carrier frequency of the high frequency quadrature amplitude modulator in the transmitter is 60GHz, and the frequency band can provide effective utilization bandwidth for OFDM with the frequency of up to 6GHz or more. The spectrum chart of the output of the two pairs of four-way I/Q signals after photoelectric conversion, optical phase shift and polarization combining treatment is shown in figure 4. From fig. 4, it can be seen that there is no OFDM information in the 125MHz bandwidths on the left and right sides of the central sideband of the modulated optical carrier 193.10THz, and the OFDM information is carried to the positive and negative first-order symmetric optical spectrum sidebands of the modulated optical carrier.
After the modulated optical carrier signal is transmitted to the far-end equipment through the SSMF, the laser light wave with the center frequency of 193.10THz and the bandwidth of 125MHz is separated through the ultra-narrow band beam splitter with the bandwidth of 1pm, and further, as can be obtained from fig. 1, the spectrum diagrams at the B, C point output from the ultra-narrow band beam splitter are shown in fig. 5 and 6 respectively. According to the illustration in fig. 1, after the two paths of split light wave signals are respectively processed by an optical attenuator, a 1:1:1 optical power divider, an optical combiner and a 1/4 dual-channel wave plate, the spectral diagrams shown in fig. 7, 8 and 9 can be respectively obtained at the corresponding point D, E, F in fig. 1.
The above process needs to be described as follows:
(1) the optical wave signal output by the optical combiner, namely the optical wave signal at the point D in the graph 1, wherein the optical wave information has no essential difference with the optical wave information at the point A in the graph 1 except that the power is different, and the optical wave signal is the modulated optical carrier signal and carries the same modulation information;
(2) the two-path polarized laser light waves with the center frequency of 193.10THz output by the 1:1:1 optical power divider are input into a 1/4 double-channel wave plate device and converted into circularly polarized light by a 1/4 wave plate, and the circularly polarized light with the center frequency of 193.10THz is pure laser light waves and does not contain any modulation information;
(3) the optical carrier signal D in fig. 1 is identical to the pure laser light wave signal at the E point, and has the same optical path length, so that the optical phases are strictly synchronous, and the center frequency is 193.10THz;
(4) the optical wave signals at two points D, E in fig. 1 enter a downlink polarization multiplexing 90-degree optical mixer to perform optical coherence demodulation, and originate from laser light waves output by the same CW laser, the center frequency is the same, the optical phases are synchronous, and pure laser at the E point is circularly polarized laser, so that the downlink 90-degree optical mixing receiving process realizes self-homodyne coherent detection and has polarization independence.
Through self-homodyne coherent demodulation with optical polarization independence, the downlink polarization multiplexing 90-degree optical mixer inputs two pairs of four-path photon radio frequency I/Q signals to a downlink diversity photoelectric detector to realize photoelectric detection conversion processing, and then 4x4MIMO wireless signal transmission can be realized according to the processing mode of FIG. 12. Namely: the self homodyne coherent detection receiving of the optical fiber communication can be realized at the rear end of the downlink diversity photoelectric detector, and meanwhile, the downlink wireless 4x4MIMO signal transmission can be directly realized without complex digital signal processing.
As shown in fig. 1, the two-way photon radio frequency quadrature modulation MQAM-OFDM system of self-homodyne coherent detection, the uplink signal processing and transmission process is as follows:
the spectrum of the other path of pure circularly polarized laser with the center frequency of 193.10THz output by the 1/4 dual-channel wave plate device is shown in fig. 9, namely the spectrum at the F point in fig. 1. The laser light wave performs relevant signal processing and transmission as an uplink modulated light wave, and the uplink implementation is the same as the downlink implementation. The uplink implementation procedure needs to be explained as follows:
(1) local oscillation laser used for implementing self-coherent detection and reception through an uplink polarization multiplexing 90-degree optical mixer is output from a CW laser, and the spectrum is shown as figure 11, namely, the spectrum at the H point in figure 1;
(2) the same as the downlink implementation: through the self-coherent demodulation of optical polarization independence, the uplink polarization multiplexing 90-degree optical mixer inputs two pairs of four-path photon radio frequency I/Q signals to the uplink diversity photoelectric detector to realize photoelectric detection conversion processing, and then 4x4MIMO wireless signal transmission can be realized according to the processing mode of FIG. 12. Namely: the self-coherent detection and reception of optical fiber communication can be realized at the rear end of the uplink diversity photoelectric detector, and meanwhile, the uplink wireless 4x4MIMO signal transmission can be directly realized without complex digital signal processing.
Key technical principle and mathematical modeling inference
As shown in fig. 4, 5, 6, 7, 8, 9, 10, 11, which respectively correspond to schematic diagrams of the spectrum principle at the point A, B, C, D, E, F, G, H in the block diagram of the transmission system. The key technical principle and mathematical modeling inference are as follows:
(1) Periodic continuous multi-zero redundancy code insertion MQAM-OFDM mathematical model design and theoretical verification
Fig. 14 shows a mathematical model of MQAM-OFDM high-frequency quadrature IQ modulation, and the output signal expression after OFDM baseband modulation is:
wherein D is k The corresponding quantity output is output for constellation mapping, namely MQAM coding; omega 0 The zero base frequency angular frequency of the subcarrier is the angular frequency of other subcarriers which are integer multiples thereof. The output expression after high-frequency quadrature IQ modulation is:
Y＝Re{x}·cosω c t-Im{x}·sinω c t
wherein omega c The frequency-up angular frequency is modulated by high-frequency quadrature and is used for wireless MIMO carrier communication.
Then the above two expressions can be derived:
it is further possible to obtain:
it can be known that:
in turn, can be obtained:
in OFDM signal processing, if the MQAM sequence useful signal input from the front end is processed by periodic continuous multi-zero redundancy code insertion logic coding and reprocessing, namely continuous multi-zero redundancy code insertion logic precoding is performed on the middle part of each periodic coding sequence, then a series of D are provided k The symbol=0, so that the multiple subcarriers on the left and right sides of the middle frequency band in OFDM modulation and the continuous multiple zero redundancy codes are in one-to-one correspondence to implement the relevant "zero" logic operation processing, and the Y signal after "zero redundancy code pattern insertion" can be expressed by using a mathematical model as:
from the above Y * In the mathematical model we can get a series of angular frequencies: -k (omega) 0 +ω c )、-(k-1)(ω 0 +ω c )、-(k-2)(ω 0 +ω c )、······、-m(ω 0 +ω c )、0、0、0、0、0、······、0、0、······、0、0、0、0、0、m(ω 0 +ω c )、······、(k-2)(ω 0 +ω c )、(k-1)(ω 0 +ω c )、k(ω 0 +ω c ) Angular frequencies occur in pairs with multiple pairs of angular frequencies in the middle being zero.
The angular frequencies and bandwidths used by the corresponding signals form a spectrogram of OFDM modulation onto a high-frequency carrier, and one obvious characteristic of the OFDM spectrogram modulated onto the high-frequency carrier is that the middle frequency spectrum is free because of a series of zero angular frequencies in the middle, so that the useful signals are not substantially involved in transmission, and the optical bandwidths of 125MHz on the left and right sides of the center of a laser carrier with the center frequency of 193.10THz in photon radio frequency modulation do not carry MQAM-OFDM radio frequency carrier information, so that the rationality of the design of fig. 3 and 4 is further verified. The center frequency of the orthogonal high-frequency carrier wave in the invention is 60GHz, namely omega c The wireless carrier effective utilization bandwidth is up to more than 10% of the carrier center frequency value, namely: the effective utilization wireless bandwidth can reach more than 6GHz, the bandwidth of the vacant 125MHz is far less than the effective utilization bandwidth of 6GHz, and the ratio of the vacant bandwidth is as follows: 125/1024/6 is approximately equal to 2%, namely, ultra-high sensitivity self-differential coherent detection receiving can be realized by sacrificing 2% of very few wireless bandwidth, a laser source is provided for uplink transmission, and a local oscillator laser source is provided for uplink and downlink coherent detection receiving.
(2) Mathematical model design and theoretical verification of photon radio frequency wave
The MZM photoelectric modulation in the invention realizes modulation by controlling the phase of a laser carrier signal by using a radio frequency local oscillation driving signal. If E in (t) and V (t) represent the addition of a continuous laser carrier signal and a local oscillator RF modulation signal, respectively, E out (t)＝E in (t)exp[j φ V(t)]Where phi is the phase offset value and the normalized number of V (t) is between 0 and 1.
If E in (t) and V (t) represent the addition of a continuous laser carrier signal and a local oscillator RF signal, ω c Representing the angular frequency of the laser light, the following can be given:
E in (t)＝E c ·cos(ω c ·t) (1)
V(t)＝V m ·cos(ω RF ·t+θ) (2)
the phase modulator output is:
E out ＝E c ·cos(ω c ·t)·exp[j·φ·V m ·cos(ω RF ·t+θ)] (3)
the output of the modulator can also be expressed in another refinement:
E out (t)＝E c ·cos[ω c ·t+γ·cos(ω RF ·t+θ)] (4)
in the above formula (4), γ=pi·v m /V π For the modulation depth of the modulator, V π Is half-wave voltage omega RF Is the angular frequency of the radio frequency modulated signal.
Let the two optical phase modulated output signals before the polarization beam combiner of fig. 1 be E respectively 1out (t) and E 2out (t), and let θ=0, then according to equation (4):
E 1out (t)＝E c ·cos[ω c ·t+γ·cos(ω RF ·t)] (5)
E 2out (t)＝E c ·cos[ω c ·t+γ·cos(ω RF ·t+π/2)] (6)
will E 1out (t) and E 2out (t) developed using the Bessel formula:
if more terms of the Bessel function are taken, more trigonometric functions of different angular frequencies can be obtained, thus E is combined by the polarization beam combiner 1out (t) and E 2out (t) after coupling, ω with CW laser light is obtained c As the central angular frequency point, the left and right sides of the central angular frequency point are respectively modulated by radio frequency signals omega RF The spectral distribution of the angular frequency spread of multiples of (2) is thus obtained
Because the powers of the spectral sidebands above the second order are very small and can be ignored relative to the power of the zero-order central spectral sidebands, taking the first term of the Bessel function as an example, E can be further expanded 1out (t) and E 2out (t) obtaining:
E 1out (t)＝E c {cos(ω c t)j 0 (γ)+2cos(ω c t)[-j 0 (γ)cos(0)]+2sin(ω c t)[-j 1 (γ)cos(ω RF t)]}
further simplification of E by utilizing periodicity and parity properties of sine and cosine functions 1out (t) and E 2out (t) obtaining:
E 1out (t)＝E c {-cos(ω c t)j 0 (γ)-2sin(ω c t)[j 1 (γ)cos(ω RF t)]}
E 2out (t)＝E c {3cos(ω c t)j 0 (γ)-2sin(ω c t)[j 1 (γ)sin(ω RF t)]}
further reduction of E by means of the integrated and difference properties of sine and cosine functions 1out (t) and E 2out (t) obtaining:
E 1out (t)
＝E c {-cos(ω c t)j 0 (γ)-2sin(ω c t)[j 1 (γ)cos(ω RF t)]}
＝E c {-cos(ω c t)j 0 (γ)-j 1 (γ)[sin(ω c t+ω RF t)+sin(ω c t-ω RF t)]}
＝E c {-cos(ω c t)j 0 (γ)-j 1 (γ)[sin(ω c +ω RF )t+sin(ω c -ω RF )t]}
E 2out (t)
＝E c {3cos(ω c t)j 0 (γ)-2sin(ω c t)[j 1 (γ)sin(ω RF t)]}
＝E c {3cos(ω c t)j 0 (γ)-j 1 (γ)[cos(ω c t+ω RF t)-cos(ω c t-ω RF t)]}
＝E c {3cos(ω c t)j 0 (γ)-j 1 (γ)[cos(ω c +ω RF )t-cos(ω c -ω RF )t]}
the following is described for the two formulas:
(1) after the photon radio frequency MQAM-OFDM carrier wave enters the self-coherent detection receiving end, only the zero-order central angular frequency of the optical carrier wave is kept to be omega by optical filtering c Spectral sidebands and optical carrier center angular frequency omega c ±ω RF The center frequency of the optical carrier is 193.10THz and the center frequency of the wireless carrier is 60GHz, so that the center frequency percentage of the positive and negative first-order spectral sidebands which implement self-coherent reception at a coherent detection receiving end is 193.10+0.06= 193.16THz and 193.10-0.06= 193.04THz;
(2) the photon radio frequency MQAM-OFDM carrier wave enters the ultra-narrow band beam splitter and carries out 125MHz ultra-narrow band-pass filtering treatment, and because the 125MHz bandwidth is far smaller than the bandwidth of 60+60=120 GHz between the center frequencies of positive and negative first-order spectrum sidebands, the output of the ultra-narrow band beam splitter does not contain the related information of the positive and negative first-order spectrum sidebands of the optical carrier wave, and only the zero-order center angular frequency omega of the optical carrier wave is reserved c The spectral side information, i.e. the optical carrier information at which the light is output by the ultra-narrow band beam splitter, is:
E 1out (t)+E 2out (t)＝3E c cos(ω c t)j 0 (γ)-E c cos(ω c t)j 0 (γ)＝2E c cos(ω c t)j 0 (γ)
(3) the MQAM-OFDM modulated signal has its central 125MHz spectrum freed by 'continuous multi-zero redundancy code insertion' and not substantially involved in information transmission, and is filtered by the ultra-narrow band beam splitter to output omega c For a pure laser light wave signal with a central angular frequency and a bandwidth of 125/2=62.5 MHz, namely: the filtered output is clean laser spectral information from (193.10 THz-62.5 mhz=) 193.0000275THz to (193.10 thz+62.5 mhz=) 193.1000625THz, i.e. as shown in fig. 6.
(3) Self-coherent photon radio frequency detection receiving mathematical model and theoretical derivation
Suppose E S For polarization multiplexing the useful signal to be demodulated at the input of the 90 DEG optical mixer, E LO For polarization multiplexing the local oscillation laser signal at the input end of the 90-degree optical mixer,
the combined complex-valued photocurrent is output to the diversity photodetector I, Q, so that the optical signal E at the four-way output end of the polarization multiplexing 90-degree optical mixer can be obtained 1 、E 2 、E 3 、E 4 The characterization values are respectively:
after the four optical signals are input into the photoelectric diversity detector, the four optical signals pass through four photoelectric detection planes PD 1 、PD 2 、PD 3 、PD 4 Implementing photoelectric detection, the photocurrents of which are respectively I 1 、I 2 、I 3 、I 4 Next we can further get:
in this way, the photocurrent I generated therein is detected in photoelectric diversity I (t)、I Q (t) is:
I I (t)＝I 1 -I 2 ＝2Re{E S (E LO ) * }；
I Q (t)＝I 3 -I 4 ＝2Im{E S (E LO ) * }；
where Re represents the real part of the function and Im represents the imaginary part of the function; in this way we can further get
The method comprises the following steps:
and E is S ＝E r +n 0 Wherein E is r Is the received vector signal portion, n 0 Is to amplify the spontaneous scattering noise part, thus |E can be obtained S | 2 ＝|E r | 2 +|n 0 | 2 +2Re{E r (n 0 ) * -a }; and local oscillation laser light wave |E LO | 2 ＝I LO [1+I RIN (t)]Wherein I LO 、I RIN (t) is the average power and Relative Intensity Noise (RIN) portions of the local oscillator laser, respectively.
Therefore, we have:
namely:
downlink in the present invention: after receiving the photon radio frequency orthogonal MQAM-OFDM signal transmitted from the transmitting end, the optical communication receiving end enters a downlink polarization multiplexing 90-degree optical mixer and a downlink diversity photoelectric detector to implement photon radio frequency signal phase synchronization self-locking self-homodyne coherent detection processing according to a downlink signal processing implementation mode, and then the photon radio frequency orthogonal MQAM-OFDM signal with the center frequency of 193.10THz and a narrow linewidth laser light wave with the center frequency of 193.10THz are demodulated by a downlink high-speed orthogonal demodulator and a downlink high-speed digital signal processing module to obtain a downlink high-speed digital baseband signal. In the receiving and detecting process, the photon radio frequency orthogonal MQAM-OFDM signal with the center frequency of 193.10THz is E in the mathematical modeling and pushing process r The narrow linewidth laser wave with the center frequency of 193.10THz is E in the mathematical modeling and pushing LO ，E r And E is LO Like the transmission optical path which is from a CW laser and is in the whole downlink, the photon radio frequency orthogonal MQAM-OFDM signal coherent detection does not independently introduce a laser local oscillation signal, namely the downlink self-homodyne coherent detection demodulation receiving of phase synchronization self-locking is realized.
Uplink in the present invention: the uplink photon radio frequency orthogonal MQAM-OFDM signal with the center frequency of 193.10THz transmitted by SSMF enters an uplink polarization multiplexing 90-degree optical mixer, and is self-coherent detected with a local oscillator laser signal which is branched from CW laser with the center frequency of 193.10THz through the uplink polarization multiplexing 90-degree optical mixer and an uplink diversity photoelectric detectorDemodulation processing is carried out, and then an uplink high-speed digital baseband signal is demodulated through an uplink high-frequency orthogonal demodulator and an uplink high-speed digital signal processing module. In the receiving and detecting process, the uplink photon radio frequency orthogonal MQAM-OFDM signal with the center frequency of 193.10THz is E in the mathematical modeling and pushing process r The narrow linewidth local oscillation laser signal with the center frequency of 193.10THz is E in the mathematical modeling and pushing LO ，E r And E is LO The method is same as a CW laser, and the laser local oscillation signal is not independently introduced in the photon radio frequency orthogonal MQAM-OFDM signal coherent detection, so that the uplink self-coherent detection demodulation reception is realized.
In the uplink and downlink transmission in the present invention, the following steps:
we can learn that: amplified spontaneous scattering noise n of received photon radio frequency quadrature MQAM-OFDM signal with center frequency of 193.10THz 0 And Relative Intensity Noise (RIN) current versus complex-valued photocurrent
Is a contribution, so that the relative intensity noise of local oscillation laser light wave with the uplink and downlink central frequency of 193.10THz can be slightly deteriorated to improve ∈>
Numerical values, and thus improve the bit error rate of high-speed digital signal processing. For example, the filter characteristic of the ultra-narrow band beam splitter can be utilized to slightly widen the filter bandwidth of the local oscillation laser light wave channel with the center frequency of 193.10THz so as to properly improve the relative intensity noise value; the filtering function of EDFA after signal amplification can be utilized to slightly widen the filtering bandwidth to increase the relative intensity noise value to improve the complex-valued photocurrent>
Thereby moderately improving the transmission and connection of the whole systemAnd (5) performance is achieved. Of course, at this time, the bandwidth of the local oscillation laser optical wave signal after filtering by the functional devices is slightly increased, and the average power part (i.e.) LO ) Thereby further improving the complex-valued photocurrents I to (t), thereby improving the bit error rate of high-speed digital signal processing.
The above embodiments are only for the purpose of fully disclosing and not limiting the invention, all changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Claims (6)
1. A signal processing implementation method of a self-homodyne coherent detection two-way photon radio frequency transmission system, characterized by comprising the following steps:
the laser light wave output by the CW laser is divided into two parts, one part is used for modulating downlink optical carrier signals, and the other part is used for detecting and receiving local oscillation laser signals used for uplink coherent optical signals; wherein, the liquid crystal display device comprises a liquid crystal display device,
the signal processing method of the downlink is as follows:
(1) The laser wave used for modulating the downlink optical carrier signal is subjected to laser wave linear polarization processing through a first polarization beam splitter, and then is modulated by two pairs of I/Q signals output by a high-frequency orthogonal MQAM-OFDM downlink transmitter through MZM-1 and MZM-2 respectively; (2) The modulated optical carrier signal is processed by 90-degree phase shift and then is combined with the other modulated optical carrier signal through a first polarization beam combiner, then signal amplification is carried out through an EDFA, and then the modulated optical carrier signal is transmitted to an ultra-narrow band beam splitter through a first SSMF; (3) The modulated optical carrier signal is separated into a positive and negative first-order spectrum sideband light wave signal B and a center spectrum sideband light wave signal C with the center frequency of 193.10THz and the bandwidth of 125MHz by a 1pm bandwidth ultra-narrow band beam splitter; (4) The positive and negative first-order spectrum sideband light wave signals B are input into an optical combiner after passing through an optical attenuator, the center spectrum sideband light wave signals C are divided into three paths through a 1:1:1 optical power divider, one path of signals is input into the optical combiner, and the other two paths of signals are input into a 1/4 double-channel wave plate device; (5) The optical wave signal D output by the optical combiner and the optical wave signal E of pure circularly polarized laser with the center frequency of 193.10THz output by the 1/4 double-channel wave plate device are input to a downlink polarization multiplexing 90-degree optical mixer, and four paths of output of the downlink polarization multiplexing 90-degree optical mixer are input to a downlink diversity photoelectric detector; (6) The four paths of output sequences of the downlink diversity photoelectric detector are processed by a downlink high-frequency orthogonal demodulator and a downlink high-speed digital signal processing module, and then a downlink high-speed digital baseband signal is demodulated;
the uplink signal processing method is as follows:
A. the other path of optical wave signal F of the pure circular polarized laser with the center frequency of 193.10THz output by the 1/4 double-channel wave plate device is subjected to laser optical wave linear polarization treatment through a second polarization beam splitter, and then is modulated by two pairs of I/Q signals output by a high-frequency orthogonal MQAM-OFDM uplink transmitter through MZM-3 and MZM-4 respectively;
B. the modulated optical carrier signal is combined with the other modulated optical carrier signal through a second polarization beam combiner after being subjected to 90-degree phase shift treatment, and then the modulated optical carrier signal is transmitted to an uplink polarization multiplexing 90-degree optical mixer through a second SSMF; C. local oscillation laser used for implementing self-coherent detection and receiving by the uplink polarization multiplexing 90-degree optical mixer is output by a CW laser, and the uplink polarization multiplexing 90-degree optical mixer inputs two pairs of four-way photon radio frequency I/Q signals to an uplink diversity photoelectric detector to realize photoelectric detection conversion treatment; D. four paths of output sequences of the uplink polarization multiplexing 90-degree optical mixer are processed by an uplink diversity photoelectric detector, an uplink high-frequency orthogonal demodulator and an uplink high-speed digital signal processing module to demodulate an uplink high-speed digital baseband signal.
2. The method according to claim 1, wherein the process of generating two pairs of I/Q signals by the high frequency orthogonal MQAM-OFDM downstream transmitter and the high frequency orthogonal MQAM-OFDM upstream transmitter is as follows: the accessed high-speed digital baseband signals are subjected to serial-parallel conversion through an ultra-high-speed serial-parallel conversion output device, and two paths of signals are output to a first pair of I/Q signal generating circuits and a second pair of I/Q signal generating circuits; the first pair of I/Q signal generating circuits sequentially perform MQAM sequence coding, OFDM modulation, double-path low-pass cut-off filtering module, space-time coding, high-frequency quadrature amplitude modulation and asymmetric electric signal processing on input signals and output first pair of I/Q signals; the processing procedure of the second pair of I/Q signal generating circuits is the same as that of the first pair of I/Q signal generating circuits, and the second pair of I/Q signals are output; the ultrahigh frequency local oscillation source provides oscillation sources for high frequency quadrature amplitude modulators in a first pair of I/Q signal generating circuits and a second pair of I/Q signal generating circuits, and space-time encoders in the first pair of I/Q signal generating circuits and the second pair of I/Q signal generating circuits are connected with each other.
3. The method according to claim 2, wherein in the process of generating two pairs of I/Q signals by the high frequency orthogonal MQAM-OFDM downstream transmitter and the high frequency orthogonal MQAM-OFDM upstream transmitter respectively: before OFDM modulation, the MQAM sequence useful signal input at the front end is subjected to periodic continuous multi-zero redundancy code insertion logic coding reprocessing, so that a plurality of subcarriers at the left side and the right side of the middle frequency band in OFDM modulation are subjected to relevant zero logic operation processing in one-to-one correspondence with the continuous multi-zero redundancy codes, and due to the fact that the periodic continuous multi-zero redundancy codes are inserted, the OFDM frequency spectrum in each period can be free of 125MHz bandwidth in the middle to participate in useful signal transmission insubstantially; the high frequency carrier frequency of the high frequency quadrature amplitude modulator is 60GHz, and the frequency band can provide effective utilization bandwidth for OFDM of up to 6GHz or more.
4. A signal processing implementation method according to any one of claims 1 to 3, wherein in the step (6) or the step D, four outputs of the downlink diversity photodetector or the uplink diversity photodetector are further subjected to the following processing: each output of the downlink diversity photoelectric detector or the uplink diversity photoelectric detector is subjected to out-of-band spurious suppression filtering treatment, amplified by radio frequency power and then transmitted by an antenna.
5. The signal processing implementation method according to claim 4, wherein the signal processing real-time method further comprises a step of receiving a transmission signal, comprising: signals are received through four antennas and are respectively input to four input ends of the two-channel out-of-band spurious suppression filter; two paths of output signals of the double-channel out-of-band spurious suppression filter are processed by a first path of decoding circuit and a second path of decoding circuit respectively; the first path of decoding circuit sequentially processes the received signals by a high-frequency quadrature amplitude demodulator, a space-time decoder, an OFDM demodulation processing module and an MQAM sequence decoding processing module; the processing procedure of the second path decoding circuit to the received signal is the same as that of the first path decoding circuit; the signals processed by the first path of decoding circuit and the second path of decoding circuit are processed by an ultra-high speed parallel-serial conversion output device and then output high-speed digital baseband signals; the ultrahigh frequency local oscillation source provides an oscillation source for high frequency quadrature amplitude demodulation in the first path of decoding circuit and the second path of decoding circuit, and space-time encoders in the first path of decoding circuit and the second path of decoding circuit are connected with each other.
6. The signal processing implementation method according to claim 1, wherein during the execution of the step (2): the signal transmission bandwidth of the ultra-narrow band beam splitter is moderately increased, so that the local oscillator laser light wave signal bandwidth with the center frequency of 193.10THz is widened, and the relative intensity noise value is improved; the filter bandwidth is moderately increased to improve the relative intensity noise value through the filter function of the EDFA after the signal amplification, thereby improving the complex-valued photocurrent of the diversity photodetector I, Q after the signal output and the combination
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