| In recent years,the rapid development of mobile communication industry has brought great convenience to people's life.In the era of "Internet plus" and big data booming in China,the demand for transmission capacity and transmission speed of mobile communica-tion is increasing.Millimeter wave(mm-wave)and terahertz(THz)band have rich spectrum resources,which will play an important role in the comprehensive application of "5g+AI"and the next generation of high-speed mobile communication.However,millimeter wave and terahertz signals are easily affected by various damages in the wireless transmission process due to their high frequency,which limits the transmission distance.Radio over fiber(RoF),which combines the advantages of optical fiber communication and wireless commu-nication,can meet the requirements of future communication network for communication bandwidth,transmission distance and mobility at the same time,has become a research hotspot in today's society.In this paper,the theory and key technologies of photonic mil-limeter/terahertz communication are studied.The millimeter wave generation system is optimized by structure improvement,algorithm optimization and device reduction,and the loss in the signal transmission process is compensated by digital signal processing(DSP),which improves the spectral efficiency and transmission capacity of the system.Then,the adaptive millimeter/terahertz wave technology is explored The technology innovation of the optical wireless system is carried out in three aspects:frequency diversification,mod-ulation format adaptation and beam tracking self feedback.The whole system seamlessly integrates optical fiber communication and wireless communication,improves the available spectrum resources in the transmission process,overcomes the possible fracture problem in optical fiber transmission,and realizes the high-speed and low-cost optical fiber wireless integration scheme.The main work and innovations are as follows:1.A new structure of generating optical frequency comb source is proposed and proved by experiments,which can be used for multi carrier modulation in optical transmission sys-tem.In this scheme,an electrically absorption-modulated laser and a phase modulator are connected,and the two are driven and synchronized using a common sinusoidal radio fre-quency signal.In this paper,the best operating range of spectral flatness with power fluc-tuation less than 3 dB is obtained by VPI simulation.Based on this experiment,10 flat top frequency locked optical frequency combs are generated,and the frequency interval of each carrier is 12.5 GHz.Using the generated comb source,millimeter wave signals with 3.125 Gb/s and 12.5 Gb/s On-Off-Keying(OOK)intensity modulation can be transmitted over 20 km standard single mode fiber(SSMF).2.A novel and simple method to generate D-band single sideband(SSB)frequency multiplication vector signal is proposed and experimentally verified.The millimeter wave generated by the system can reach 210 GHz,which has entered the terahertz field.In this scheme,a single driven Mach-Zehnder modulator(MZM)and a push-pull MZM are cas-caded.The first MZM has a driving signal at the frequency of 20 GHz,and an optical frequency comb with six flattened carriers is generated.Then,a push-pull MZM driven by 10 GHz SSB vector signal is used to realize the single sideband modulation.After hetero-dyne beat by photodiode(PD),D-band SSB vector millimeter wave signals with frequencies of 130 GHz and 150 GHz are generated.The 4 Gbaud D-band QPSK/16QAM mm-wave signals generated based on this scheme are respectively transmitted on a 10 km/25 km single-mode optical fiber plus 1 m wireless link,and the calculated bit error ratio(BER)can reach a 7%hard decision forward error correction(FEC)threshold of below 3.8×103.3.A D-band millimeter wave signal generation scheme based on optical carrier sup-pression and single sideband modulation is proposed and verified.The scheme saves the precoding process at the transmitter and does not need any filter,so the whole system is simplified.Firstly,an intensity modulator driven by a 50 GHz RF signal(fRF)is used to generate two carriers with frequency interval of 2×fRF,which realizes the process of op-tical carrier suppression.Then,another I/Q modulator driven by a 30 GHz RF signal is used to generate a single sideband vector signal through independent sideband modulation.After using D-band photon-mixer for detection,130 GHz vector millimeter wave is finally generated.After that,we carried 4 Gbaud/8 Gbaud QPSK information using the D-band millimeter wave generated by the system,and transmitted it over 22.5 km SSMF and 1 m RoF links.Finally,the transmission results are analyzed,and the BER performance of hard/-soft decision forward error correction threshold based on two different signal transmission rates is given.4.An adaptive N2-QAM modulation format W-band millimeter wave vector signal generation technique for optical millimeter wave communication system is proposed and experimentally verified.Using two intensity modulators MZM,parallel phase shifter and at-tenuator,and a single optical mixer,the process of synthesizing N2-QAM millimeter wave vector signal from two N-ASK signals is realized.This scheme saves Digital-to-Analog Converter(DAC)and additional digital signal processing at the transmitter,and can obtain double bit rate at the user.Taking N=2 as an example,this paper uses two 2-ASK signals to generate 80 GHz 4 QAM W-band millimeter wave,and completes its high-performance transmission over lm wireless link.The measured BER curve reaches 7%hard decision forward error correction threshold of less than 3.8 × 103.5.The application prospect of terahertz wave is explored,and a full band transmitter with 470 GHz bandwidth is designed and experimentally proved,which covers Q,V,W,D band millimeter wave and up to 510 GHz terahertz wave signal.The scheme combines independent millimeter wave channel and terahertz channel,which greatly improves the flex-ibility of wireless network and promotes the development of power amplifier.This scheme can generate multiple frequency bands of millimeter wave and terahertz wave at the same time,and integrates a broadband multi antenna transmission system and a photon-mixer with high bandwidth and dynamic range,which realizes adaptive frequency band switching and dynamic wireless transmission.It has great application value for 5G and 6G.6.A positioning technology based on machine learning algorithm for millimeter wave/terahertz beam tracking is proposed,which can provide accurate azimuth for wireless base station to meet the needs of adaptive beamforming.Due to the high carrier frequency of millimeter wave/terahertz wave,the attenuation is large in the atmosphere.Beamforming can reduce the beam width of millimeter wave/terahertz wave,so it is necessary to know the user's exact position for beamforming.In this paper,combined with the application of indoor high frequency radio waves,an innovative design of indoor positioning system based on artificial neural network(ANN)is proposed to serve the beam shaping.The accuracy of less than 1cm obtained by experiments is the highest accuracy solution that indoor positioning system can achieve.It will provide a new solution for 5G and the next generation of wireless beam tracking,which is of great significance to realize the high efficiency and large capacity transmission of optical wireless communication system. |
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