1.School of Communication and Information Engineering, Xi’an University of Posts and Telecommunication, Xi’an 710121, China 2.School of Electronics and Information, Northwestern Polytechnical University, Xi’an 710072, China 3.State Key Laboratory of Integrated Service Networks, Xi’an University of Electronic Science and Technology, Xi’an 710071, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 61971348, 61201194), the International Scientific and Technological Cooperation and Exchange Program in Shaanxi Province, China (Grant No. 2015KW-013), and the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 16JK1711).
Received Date:24 June 2020
Accepted Date:13 September 2020
Available Online:22 January 2021
Published Online:05 February 2021
Abstract: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 (${S_{\rm{1}}}$), medium snow (${S_{\rm{2}}}$), heavy snow (${S_{\rm{3}}}$) and blizzard (${S_{\rm{1}}}$). 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 (${S_{\rm{1}}}$) 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 (${S_{\rm{2}}}$) 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. Keywords:quantum communication/ snowfall intensity/ extinction coefficient/ survival function