Application Research Of Multi-dimensional And Multi-order Modulation Signals In Full-duplex FSO Transmission Syste

In recent years,a variety of new Internet data services are rapidly spreading and applying.Although the traditional optical network uses optical fiber as the physical channel to support high-speed and largebandwidth full-duplex signal transmission process,the poor mobility performance and high construction cost are sometimes difficult to achieve flexible access to end users under special terrain conditions,and the optical cable laying has certain geographical limitations,which can’t meet the actual application requirements.Free Space Optical Communication(FSO)is a wireless communication system that supports high-speed optical signal transceiver,transmission and access between Optical Line Terminal(OLT)and Optical Network Unit(ONU).It has high transmission rate,large transceiver capacity,strong anti-interference,good confidentiality,short construction period,no municipal license plate,easy installation and upgrade.The regional application advantages that are not easy to lay optical cables and require high-speed access to multiple types of information have been highly valued by the industry.However,since the transmission channel in the FSO system is an atmospheric channel in free space,various molecules and solid and liquid aerosol particles in the atmosphere will lead to phenomena such as scattering,absorption and eddy current,especially the negative impact of atmospheric turbulence effect will reduce the effective receiving quality of the signal.Therefore,this paper optimizes the multi-dimensional multi-order modulation format and photoelectric device parameter configuration to better adapt to the working window of the atmospheric channel to realize the signal transceiver,transmission and access,and forms a full-duplex FSO communication system that adapts to various weather conditions and is not limited by special topography.It has important research significance and practical value.This paper analyzes the principle and structure of FSO communication system,and expounds the basic working principle of modulation and demodulation of phase shift keying modulation technology,quadrature amplitude modulation technology,pulse amplitude modulation technology and orthogonal frequency division multiplexing modulation technology.On the basis of the above research work,the free space full-duplex channel model is modeled and analyzed,and its feasibility is verified by simulation experiments.The uplink and downlink bidirectional transmission process is emphatically studied,and the transceiver and access characteristics of several modulation signals are studied.The main research process and results are as follows:A 10 Gbit/s downlink 4-order Pulse Amplitude Modulation(PAM4)signal and an uplink non return to Zero(NRZ)signal are designed.A 1.5Gbit/s downlink using 67% RZ-PAM4 signal and uplink using Alternate Mark Inversion(AMI)phase modulation signal is designed.A 100Gbit/s downlink hybrid16PSK/256QAM-OFDM(Phase Shift Keying/Quadrature Amplitude ModulationOrthogonal Frequency Division Multiplexing)signal and an uplink Duobinary(DB)signal are designed.A 120Gbit/s downlink dual-polarization 64-ary quadrature amplitude modulation(DP-64QAM)signal and uplink differential quadrature phase shift keying(DQPSK)signal are designed.A full-duplex FSO communication system with 10 Gbit/s downlink Manchester intensity modulated signal and uplink DB signal is designed.The bidirectional transmission and transmission characteristics of the uplink and downlink signals through 100 m,300m,500 m and 1km free space channels under different weather conditions are studied.At the same time,the constellation diagram of 125Gbit/s DP-64 QAM signal transmitted in free space channel without bit error rate(BER)when combining probabilistic amplitude shaping(PAS)technology is studied.The results show that the system designed in this paper can significantly improve the spectrum utilization rate.The uplink and downlink signals have strong atmospheric turbulence resistance effect,and both achieve BER performance lower than the hardware decision forward error correction(HD-FEC)threshold.