Performance Analysis Of Reconfigurable Intelligent Surface Assisted FSO Communication Systems

With the advent of the era of Internet of Things,an increasing number of intelligent devices are connected to wireless network.This requires the mobile network to meet the service standards of high throughput,ultra-reliability and low delay.Due to the limitation of bandwidth and data rate,the radio frequency(RF)technology fails to meet the needs of the current network.In recent years,free space optical(FSO)technology is regarded as an alternative to RF technology with the advantages of high bandwidth,economy,and easy installation.However,the performance of FSO communication systems is vulnerable to effect of the environment and communication distance.And demanding conditions for line of sight(LOS)are required.In order to make full use of the strengths of the two technologies,the mixed FSO-RF system by applying the cooperative communication technology was proposed by researchers.In addition,the reconfigurable intelligent surface(RIS)can create a real-time reconfigurable propagation environment by controlling the amplitude,phase and even polarization of the impinging signal without complex coding and decoding algorithms.In order to further improve the perform ance of mixed FSO-RF systems and reduce its power consumption,this thesis researches an RIS-based dual-hop FSO-RF system.On the other hand,researchers proposed an RIS reflecting FSO signals,which is called optical reconfigurable intelligent surface(ORIS)in this thesis.However,the early work on ORIS-assisted FSO systems only considered the pointing error.Therefore,this thesis further studies an ORIS-aided FSO system affected by atmospheric turbulence and pointing error,and provides numerical analysis results.The main contributions are as follows:(1)This thesis proposes a dual-hop RIS-based mixed FSO-RF system with decode-and-forward(DF)relay.It also take into account the following conditions that the first FSO link obeys atmospheric turbulence fading,which modeled by Gamma-Gamma distribution,with pointing errors,and that the RF link suffers from Rayleigh fading,and the RIS is used to improve the channel environment.On this basis,the outage probability,the bit error rate(BER)with DBPSK-SIM and the average channel capacity of the whole system are calculated.In addition,the influence of different parameters on system performance are obtained by observing the changes of performance curses,such as the number of reflecting metasurfaces of the RIS,atmospheric turbulence,and pointing errors and so on.The asymptotic results are given to obtain the diversity gain of this system.The results show that the system performance is affected by the FSO link when the RF link is at high SNR.Finally,the outage probability performance loss of discrete phase shift and continuous phase shift is compared.(2)In order to improve the performance of the FSO system,we propose an ORIS-assisted FSO communication system,where the ORIS is used to create the LOS transmission environment for the FSO link and improve intelligent communication environment.Assuming the FSO link obeys the double generalized Gamma fading,this thesis adopts the Gamma random variable approximation to deduce the outage probability,BER,and channel capacity performance of this system.Furthermore,the performance curses of simulation and analytical results are drawn by Monte-Carlo simulation.And the effect of parameters on the ORIS-aided FSO system can be seen by setting multiple groups of parameters.Finally,the asymptotic outage probability is calculated,and the diversity gain of the ORIS-assisted FSO system is given.