Simulation Of Laser Transmission In Turbulent Sand Atmosphere And Its Impact On Communication Performance

Laser atmosphere wireless(Free Space Optical,FSO)communication technology is currently in the stage of rapid development,as one of the most popular communication technologies.It has the characteristics of large capacity,strong confidentiality,simple structure and low delay,etc.However,laser signals are extremely vulnerable to the transmission environment.China is one of the countries with the most serious land desertification.The transmission performance and application of the laser in sand and dust atmosphere needs special attention.In order to study the impact of the sand and dust atmosphere on the laser communication system,it is necessary firstly to study the transmission characteristics of laser in sand and dust atmosphere.The main contents include:1.In order to analysis the attenuation of laser propagating in sand and dust atmosphere,the laser scattering of sand or dust particle are calculated by Mie scattering theory.Based on log-normal distribution models,using Monte Carlo(MC)method,the multiple scattering characteristics are analyzed for laser transmitting in different visibility sand and dust atmosphere.The results shows that at a certain transmission distance,as the visibility of the sand and dust atmosphere decreases,the number of light scattering gradually increases,and the received light intensity gradually decreases.2.In order to study the time domain characteristics of the laser pulse signal in sand and dust atmosphere,the propagating state of all photons is tracked one by one with MC method,the arrival time of the received photons and the received light intensity are counted.The waveform of the Gaussian pulse deformation during the transmission in the sand and dust atmosphere can be obtained by MC method.The results show that as the visibility of sand and dust atmosphere increases,the delay and pulse broadening of the received signal decrease.The received light intensity increases with the optical wavelength increases.The pulse delay decreases as the asymmetry factor of the dust particles decreases,and increases as the scattering coefficient of the dust particles increases.3.In order to obtain more realistic communication channel characteristics of sand and dust atmosphere,based on the atmospheric turbulence fading models: logarithmic normal distribution,double Gamma distribution,and exponential Weibull distribution,in Single-Input Single-Output(SISO)system,using On-Off Keying(OOK)modulation,the influence of laser transmission through turbulent dust atmosphere on communication performance is studied.The results show that for different turbulence fading models under weak turbulence,the average bit error rate of the simulated systems is close.For different turbulence fading models under strong turbulence,the average system bit error rate varies greatly.From weak to strong turbulent in sand and dust atmosphere,Double Gamma distribution can be treated as an ideal turbulence model.4.In order to improve the transmission performance of the laser communication system in sand and dust atmosphere,the MC method is used to simulate the channel transmission matrix in each sub-link of the Multi-Input Multi-Output(MIMO)communication system.The average bit error rates of the MIMO system in different antenna numbers with OOK and Pulse Position Modulation(PPM)modulation are calculated.The results show that with the decrease of atmospheric visibility,the bit error rates of the system rapidly increase.The improvement of bit error rate by PPM modulation is better than that of OOK modulation.The transmission diversity in the MIMO system can better improve the performance of the system.