Faster-than-Nyquist Atmospheric Optical Transmission Model And Performance Analysis

With the deployment of 5G communication systems and the in-depth development of6 G communication technology,the demand for large-capacity and high-speed access technologies in information networks continues to grow.In addition,it also needs to meet artificial intelligence,virtual reality,telematics,robotics,etc.In terms of speed requirements for digital applications.Atmospheric optical communication technology is one of the alternative technologies to effectively solve the demand for high speed.Its development trend and potential have attracted great attention from various countries.However,the performance of the atmospheric optical communication system is easily affected by the atmospheric channel environment and the speed limit of actual electronic devices,which makes it difficult for the existing atmospheric optical communication technology to meet the needs of high-speed wireless communication.Therefore,in order to improve the transmission rate of the atmospheric optical communication system under the premise of limited bandwidth,the Faster-than-Nyquist optical transmission technology is proposed.As a non-orthogonal transmission technology,the Faster-than-Nyquist(FTN)optical transmission technology has a signal rate greater than the Nyquist rate.When combined with a low-order modulation format,it is used in atmospheric optical communication systems to further improve transmission performance of the communication system.However,when the optical signal is transmitted in a long-distance atmosphere,the turbulence effect caused by the atmospheric turbulence will cause the system to increase the bit error rate and reduce the channel capacity.Based on the traditional atmospheric optical communication system,this paper studies the atmospheric FTN optical transmission system using low-order modulation and FTN technology.In order to solve the problem of turbulence effect of the FTN optical transmission technology in the atmospheric turbulent channel transmission,the channel capacity and bit error performance of the FTN optical transmission system under different turbulent conditions are analyzed.In this paper,an atmospheric optical communication system by FTN rate is designed by combining quaternary phase shift keying(QPSK)and FTN technology.The atmospheric optical transmission system based on FTN-QPSK signal are given.The system model theoretically analyzes the channel capacity and performance of bit error under different scintillation factor.On this basis,the expressions of bit error rate under the log-normal atmospheric turbulence channel model are derived.Through Monte Carlo simulation numerical analysis,the channel capacity and bit error rate of the FTN-QPSK signal underdifferent turbulence and the traditional modulation QPSK signal are compared respectively.It can be seen that the proposed FTN-QPSK atmospheric light transmission system has a higher the transmission rate and spectral efficiency.when SNR is 30 dB and S.I.is 0.4,the efficiency can reach to 1.6Baud/s/Hz,it is an increase of approximately 14.2% compared to when without FTN technology is used.In addition,for the problem that the transmission performance and error performance of the system are affected by scintillation factor,it is proved that the transmission rate and error performance of the system can be effectively compromised by adjusting the value of scintillation factor.In order to further expand the applicable scope of the study and analyze the system performance under medium and strong turbulence intensity,on the basis of studying the weak turbulence channel represented by the log-normal atmospheric turbulence channel,this paper further analyzes the FTN atmospheric optical transmission system under the Gamma-Gamma turbulence channel The.Theoretically derives the expressions of its system channel capacity and bit error rate.The results of numerical analysis show that strong turbulence has a significant effect on the performance of the system after introducing FTN technology into the atmospheric optical communication system.However,under medium and weak turbulent conditions,the average capacity of the system after using FTN-QPSK technology is significantly better than that of the system without FTN technology.Compared with the system without FTN technology,although the bit error performance will be reduced in the case of weak and medium turbulence,the average capacity of the system has been significantly improved.In comparison,the loss of bit error performance is basically negligible.Therefore,the introduction of FTN technology provides a possible and effective measure for atmospheric optical communication to achieve large-capacity and high-rate transmission.