A Research Of Atmospheric Laser Communication Transmission Characteristics Based On Degree Of Polarization

Atmospheric laser communication(ALC)is a safe and efficient communication technology that uses laser beams as carriers to transmit data and information in a free space.However,the adverse effects of atmospheric channels are difficult to overcome.In atmospheric communication channels,the scattering and absorption of the atmosphere will reduce transmitted signal power,and atmospheric turbulence will cause irregular fluctuations in the refractive index.When the laser communication pulse signal is transmitted through the atmospheric channel,a multipath effect will occur because of multiple scattering,which will cause the received pulse to move backward in the time domain.Multipath effect will cause the transmission coding sequence interference.The increase of bit error rate has led to a decline in the transmission quality of atmospheric laser communications.The content of this paper is as follows:(1)Three factors affecting atmospheric transport(absorption,scattering and turbulence)are introduced.The main scattering theories(Mie scattering and Rayleigh scattering and multiple scattering)are introduced;Aerosol particles and multipath effects in the atmosphere are introduced.The polarization theory of scattering light and the Stokes vector are introduced.The principle and steps of the Monte Carlo method and the simulation process are analyzed.(2)To study the scattering of laser beams in atmospheric cloud media,through approximate the function of Mie scattering theory,we adopt the Monte Carlo method to simulate the propagation process of laser beams in the atmosphere cloud media,and obtain the waveform of the laser pulse's broadening time;The influence of parameters such as asymmetry factor,cloud physical thickness,extinction coefficients,and receiver field of view was analyzed.The paper carries out a Monte Carlo simulation experiment by using the technologies of photon tracing and Stokes Vectors' transformation.The one-to-one relationship between received laser's degree of depolarization and cloud's optical depth is obtained through setting diversity of cloud's physical depths and extinction coefficients.(3)Reducing the transmission rate of the laser communication will dealt with multipath effect.However,this will impair the performance of the high transmission.Therefore,we could directly detect degree of polarization at the receiver.It could then assure the laser communication propagation quality while achieving the fastest communication rates.According to the idea of adaptive laser communication system,PPM modulation and OOK modulation are used.Selecting different laser transmission rates and modulation patterns,it can effectively ensure the communication quality.What the paper researches on has theoretical guiding significance and application value in communication link optimization of satellite-ground laser communication and adaptive laser communication.