Research On Wireless Laser Communication System In Complex Weather Environment

Wireless laser communication(WLC)is a new broadband wireless access method.It has become a research hotspot in the global optical communication industry since the 1990 s.Compared with traditional fiber-optic communications,wireless laser communications combine the advantages of microwave and fiber optic communications with a very high signal frequency,with no significant interference from surrounding electromagnetic waves and a large capacity.The transmission speed can reach Gigabits per second,does not occupy the existing frequency band resources,and can be well applied in the "last mile" communication occasion.Although the WLC system has obvious advantages,it also has corresponding defects.Atmospheric turbulence will also cause the intensity of optical signals to fluctuate,which will affect the communication performance.In addition,we should reduce the interference of the weather environment in signal transmission as far as possible.And select the appropriate encoding and modulation formats,so that the transmission rate and bit error rate of WLC system can be guaranteed accordingly.Improving the reliability of the system,reducing the BER and overcoming the randomness error of the channel is of great significance for advancing the development of WLC technology.The research content of the thesis can be summarized as follows:1)We reviewed the current research status of the WLC system and analyzed the main factors and key technologies that affect the WLC system.From the theoretical perspective,the specific mechanism and specific form of the atmospheric wireless laser transmission have been studied.Introduce the physical properties of atmosphere and many atmospheric phenomena.Analyze the attenuation effects caused by different atmospheric phenomena based on different raindrop spectrums.2)The physical and statistical characteristics of atmospheric turbulence are explained.According to atmospheric laser transmission theory,the systematic study of the effects of atmospheric turbulence caused by strong undulations,drift of light velocity,and beam broadening on laser communications has been performed.3)The Gamma-Gamma model is introduced into the atmospheric random channel.With reference to the parameters corresponding to the actual device,a WLC system based on direct detection and coherent detection technology was set up.The constellation diagram of the DD-OFDM-WLC and CO-OFDM-WLC systems and the change trend of the BER with the atmospheric channel attenuation are compared and analyzed.