Influence of snowfall on free-space quantum channel near earth surface and parameter simulation
Authors: Nie Min , Wang Chao-Xu , Yang Guang , Zhang Mei-Ling , Sun Ai-Jing , Pei Chang-Xing ,   School of Communication and Information Engineering, Xi’an University of Posts and Telecommunication, Xi’an 710121, China,   School of Electronics and Information, Northwestern Polytechnical University, Xi’an 710072, China,   State Key Laboratory of Integrated Service Networks, Xi’an University of Electronic Science and Technology, Xi’an 710071, China
Published: January 2021

Quantum communication has the advantages of wide coverage and security, and is currently a hot research topic in the field of communication. In the process of free space quantum communication, quantum signals need transmitting at a certain height above the surface. Various environmental factors in free space, such as snowfall, sandstorms, rainfall, haze and floating dust, will inevitably affect quantum communication performance. However, so far, the influence of snowfall on the performance of quantum channels in free space near the surface has not been investigated. Thus, according to the intensity of snowfall, the snowfall is divided into four levels: light snow (<inline-formula><tex-math id="M7">\begin{document}${S_{\rm{1}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M7.png"/></alternatives></inline-formula>), medium snow (<inline-formula><tex-math id="M8">\begin{document}${S_{\rm{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M8.png"/></alternatives></inline-formula>), heavy snow (<inline-formula><tex-math id="M9">\begin{document}${S_{\rm{3}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M9.png"/></alternatives></inline-formula>) and blizzard (<inline-formula><tex-math id="M10">\begin{document}${S_{\rm{1}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M10.png"/></alternatives></inline-formula>). When the snow is falling in the air, it has an energy absorption effect on the light quantum signal, which is called the extinction effect. The different intensities of snow extinction have different effects on free space optical quantum signal. In this paper, first, a mathematical model for the extinction effects on optical quantum signal at different levels of snowfall is presented; then the quantitative relationship between snowfall and free space extinction attenuation, as well as the relationship between snowfall and channel limit survival function is established, channel capacities under different snowfall intensities, and quantum bit error rate are also given. Finally, the mathematical models of snowfall intensity, transmission distance and link attenuation, amplitude damping channel capacity, channel survival function and channel error rate are established. Simulation results show that when the snowfall intensity is 2.1 mm/d (<inline-formula><tex-math id="M11">\begin{document}${S_{\rm{1}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M11.png"/></alternatives></inline-formula>) and the transmission distance is 2.2 km, the communication link attenuation is 0.0362, the channel capacity is 0.7745, the channel survival function is 0.2329, and the channel error rate is 0.0105. When the snowfall intensity is 3.8 mm/d (<inline-formula><tex-math id="M12">\begin{document}${S_{\rm{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20200972_M12.png"/></alternatives></inline-formula>) and the transmission distance is 3.5 km, the communication link attenuation is 0.1326, the channel capacity is 0.4922, the channel survival function is 0.2099, and the channel error rate is 0.019. Thus, different snowfall intensity has different influence on the performance of free space quantum communication. Therefore, in practical applications, the communication parameters should be adjusted adaptively based on the snowfall intensity to improve the reliability of free space quantum communication.