| With the development of the air platform,the application of wireless optical communication in the slant path is gradually increasing,but the atmospheric effect still has a great impact on the performance of the current near-infrared system.Compared with near-infrared,far-infrared has stronger anti atmospheric attenuation and atmospheric turbulence ability,which is the development direction of the next generation wireless optical communication technology.Because the refractive index structure constant of slant path changes with altitude,the research based on horizontal link is not suitable for slant path.So far,there is still a lack of in-depth research on the atmospheric transmission characteristics of far-infrared in slant path,and the ground-air slant path wireless optical communication system urgently needs theoretical guidance.In this paper,the free space optical communication channel model is established,and the transmission characteristics of far-infrared light in the earth space slant path atmosphere are studied.The research work of this paper mainly includes:1?The composition of atmosphere is analyzed,and the link loss model of ground-air slant path wireless optical communication system is established.The transmission loss of far-infrared light in different zenith angle and visibility is simulated.The results show that when the zenith angle is greater than 60 °,the transmission loss of far-infrared is obviously less than that of near-infrared and mid-infrared,which shows the transmission advantage of far-infrared under large zenith angle.In high visibility,the loss of near-infrared,middle infrared and far-infrared slant path transmission is similar,but the lower the visibility is,the better the far-infrared performance is.2?The scintillation caused by atmospheric turbulence greatly affects the reliability and stability of wireless optical communication system.In this paper,based on the three-layer height spectrum and Rytov theory,the expressions of scintillation index for uplink and downlink without are derived under the condition of weak turbulence.The effects of zenith angle and transmission distance on scintillation index are analyzed.The results show that the far-infrared transmission in the weak turbulence with zenith angle greater than 30 ° can restrain the scintillation caused by turbulence to a certain extent;when the far-infrared transmission in the atmospheric turbulence channel,with the increase of the distance,the scintillation index changes little and tends to saturation gradually,that is,it can achieve a longer communication distance;the larger the receiving aperture of the farinfrared wireless optical communication system,the smaller the scintillation index.3?According to the scintillation index,the mathematical expressions of BER,outage probability and communication capacity of the ground-air slant path wireless optical communication system are derived,and the parameters affecting the system performance are analyzed.The results show that when the On-Off-keying(OOK)modulation,the BER of the far-infrared ground-air slant path wireless optical communication system decreases rapidly with the increase of the signal-to-noise ratio(SNR);If the BER of the system is to reach 10-9,the SNR of PPM modulation method is smaller than that of OOK;for far infrared wireless optical communication system,with the increase of near earth turbulence intensity and decision threshold,the performance of the system decreases the outage probability also increases,and the average carrier to noise ratio plays a major role in the average channel capacity.4 ? A channel simulation software for the ground-air slant path far-infrared wireless optical communication is developed.Through numerical simulation,it provides channel parameter prediction for the design of wireless optical communication systems.Based on the results of theoretical analysis,a set of far-infrared wireless optical communication system was also build,which relizes the transmission of voice. |
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