Research On Transmission Characteristics Of Laser Communication System Under Sand And Dust Channel

As the most promising military and civilian communication method in the future,Atmospheric laser communication has become a hot spot in global research recent years with its advantages of large communication capacity,strong confidentiality,and light weight.At the same time,the randomly distributed scattered airborne particles in the near-atmosphere,such as dust,clouds,etc.,can cause the laser beam to be affected by scattering,absorption,and attenuation.Especially in the sand and dust weather with a large number of foreign particles,this effect will cause serious distortion of the laser signal,reduce the performance of the communication system,and even lead to communication interruptions.Therefore,the transmission characteristics of laser signals in the near-Earth atmosphere has become one of the key issues that must be considered when designing an efficient and reliable laser communication system.Therefore,the transmission characteristics of laser signals in the near-Earth atmosphere has become one of the key issues that must be considered when designing an efficient and reliable laser communication system.At present,a large number of studies on the characteristics of laser transmission in sand and dust weather are based on the assumption that dust particles are assumed to be spherical or have a specific shape,which ignored the complex structure and different shapes of dust particles.Therefore,this assumption is too idealistic,which have a certain difference with the actual situation.And related experimental research shows that,the irregularity and size distribution of dust particles will cause the spatial distribution of scattered light in the sand and dust channel.In addition,the attenuation characteristics of the laser signal in the sand and dust channel are affected not only by the scattering effect but also by the absorption effect of moisture contained in the dust particles.Therefore,focusing on these issues,this dissertation analyzes the physical characteristics of the sand and dust channel firstly,and combines the radiation transmission theory and the electron scattering theory,the transmission characteristics and system performance of the laser signal in the sand and dust channel are discussed and analyzed.The work is as follows:(1)The radiative transfer equations of laser signals in dusty weather are derived using the approximate conditions of small angles and the recursive step by step method.For different wavelengths of laser signals,the variation of lightintensity with parameters such as the number of scattering,optical thickness,and asymmetry factor were studied.The results show that the received light intensity decreases with the increasing of scattering times,and increases with the increasing of optical thickness and then decreases.When the number of scattering is greater than 3,the change in received light intensity is almost 0.And when the wavelength is shorter and the asymmetry factor is smaller,the received light intensity is smaller,and the scattering effect is greater.(2)Based on the theory of electron scattering,the time delay and the broadening function of the laser pulse under dust weather conditions were deduced using the approximate conditions of small angles.The time-varying and widening of pulse signals with different wavelengths were studied with the variation of transmission distance and visibility.Meanwhile,combined with the concentration distribution function of dust particles and its complex permittivity,the attenuation expression of laser signal under sand and dust channels was deduced,the effects of different parameters such as laser wavelength,visibility,humidity,and transmission height on the change of attenuation were analyzed.The results show that the time delay and width of the pulse increase with the increasing of transmission distance,scattering albedo and scattering coefficient,and decrease with the increasing of visibility,laser wavelength and asymmetry factor.In addition,as the laser wavelength and humidity increasing,the attenuation also gradually increases.(3)The signal-to-noise ratio of the laser signal in the dust channel is deduced by using the attenuation expression.Meanwhile,the bit error ratio(BER)and the channel capacity of the system are deduced for the On-Off Keying(OOK)modulation method.Simulation analysis of the BER and channel capacity varies with atmospheric visibility,transmission distance,atmospheric humidity,and laser signal wavelength.The results show that with the increasing of water content and transmission distance and the reduction of atmospheric visibility,the BER will continue to increase,while the channel capacity will decrease.The results of this dissertation have the significances to instruct modeling the system of atmospheric laser communication,and to study the transmission characteristics of laser communication under dust weather.In addition,this dissertation also provides a certain reference value for reasonably select the laser devices in practical engineering applications.