Research On Performance Analysis Of FSO Communication System Under Various Factors And Mitigation Techniques

Free space optical(FSO)communication applies optical carrier for information transmission in free space.Due to its advantages of huge bandwidth,higher data-rate,easy deployment and license-free,FSO has been widely concerned in industry and academia.However,FSO system performance is influenced by channel estimation error,obstructions,pointing error and atmospheric turbulence,in which the system performance will be degraded.Against this background,the impact of atmospheric turbulence,pointing error,channel estimation error and link blockage on system performance is investigated.To improve the system performance,the reconfigurable intelligent surface(RIS)-assisted FSO system as well as the relaying-assisted mixed radio frequency(RF)-FSO system are proposed.The main contributions are summarized as follows:(1)Considering the impact of atmospheric turbulence,atmospheric loss,pointing error and link blockage,the system and channel model are established.The performance metrics are derived,including outage probability,average bit error rate and ergodic capacity,and the consistency of the model is verified.The analytical results are validated by simulation and demonstrate the effect of signal blockage,detection method,the strength of turbulence and pointing error on FSO system performance.(2)In the case of imperfect CSI for FSO system,the composite channel model are built considering the joint impact of atmospheric turbulence,atmospheric loss and pointing error.Using the probability density function and cumulative distribution function of channel model,the performance metrics are derived,including outage probability,bit error rate and ergodic capacity.Through numerical simulation,the influence of channel estimation error,the strength of turbulence and pointing error on FSO system performance is analyzed.(3)RIS-assisted FSO system is established by introducing RIS into FSO system.With the help of Fox’s H function and moment generating function,the channel model of RIS-assisted system is derived.Considering intensity modulation with direct detection and heterodyne detection,the expressions of performance metrics are derived by applying multivariate Fox’s H function.Finally,the impact of reflecting elements,atmospheric turbulence,detection method,pointing error and channel estimation error on FSO system is simulated and analyzed.(4)The mixed RF-FSO system with amplify-and-forward relaying is analyzed,in which RF link is subject to Rayleigh fading and FSO link is assumed to follow Fdistribution fading.Considering pointing error,the expressions of outage probability and bit error rate are derived by using Meijer’s G function,and the expression of ergodic capacity is derived by utilizing the extended generalized bivariate Meijer’s G function.Finally,the system performance is analyzed under different atmospheric turbulence,pointing error and detection method for variable-gain relay and fixed-gain relay.