Research On The Performance Of FSOC System In Atmospheric Turbulence Channel

Free-space optical communication(FSOC)has the advantages of high security,frequency bandwidth,low construction cost,rapid deployment and no need for frequency licensing.It has great market application value and has becoming a research hot spot in the field of communications.However,the optical communication link is in the atmosphere,and the light beam is affected by the atmospheric attenuation,including the absorption of particles in atmospheric and the attenuation of scattering.At the same time,atmospheric motion is also affected by atmospheric turbulence,which leads to random changes in atmospheric refractive index.It can affect the beam,such as beam spread,beam drift and light intensity flicker.The flicker of light intensity can result in a serious degradation of the beam quality,which affects the reliability and stability of the optical communication system.Based on the above problems,this paper mainly studied the mechanism of the signal beam affected by the atmospheric turbulence,analyzed the performance of the FSOC system under the atmospheric turbulence channel and carried out the corresponding numerical simulation.It mainly includes the following two parts:(1)In the atmospheric turbulence channel,we had used the modified Rytov theory and the Meijer G function to derive the closed expressions of opticalcommunication interruption probability in planar wave,spherical wave and Gaussian wave atmospheric turbulent channel Gamma-Gamma distribution models.The beam skew path transmission theory was studied and analyzed.Based on the model of ITU-R atmospheric structure model varying with height,the influence of the atmospheric turbulence channel on the interruption probability of plane wave,spherical wave and Gaussian wave as the carrier light source was simulated numerically.And the main influence of atmospheric turbulence on FSOC performance was analyzed.(2)This article selected the appropriate modulation method from the view of the modulation signal,thereby reducing the impact and improving the communication quality.The error symbol rate performance of the optical communication system in the turbulent channel was studied under different modulation methods.By analyzing and deriving the encoding method of the MPPM modulation and deriving the exponential Weber channel model,the error symbol rate during demodulation of MPPM hard-soft decisions was analyzed.On the above basis,this paper proposed an improved multi-pulse modulation scheme(IMPPM).Through experiments,the error symbol rate of wireless optical communication in the turbulent channel under MPPM and IPPPM modulation methods was compared and analyzed.