降雨背景下诱骗态协议最优平均光子数的变色龙自适应策略

为了应对降雨给采用诱骗态协议的量子通信系统带来的突发性干扰,根据降雨分布模型和退极化信道的特性,本文提出了基于变色龙算法的每脉冲最优平均光子数自适应策略;建立了降雨强度、链路距离与最优平均光子数之间的自适应关系;并对采用变色龙算法前后,系统的性能参数进行了比较.仿真结果表明,当降雨强度J为30 mm/24 h、链路距离L为30 km时,通过采用变色龙算法,系统的安全密钥生成率由2×10~(-4)提高到3.5×10~(-4);当J为60 mm/24 h,L为20 km时,系统的信道生存函数值由0.52提高到0.63;当要求生存函数不低于0.5时,系统能够应对的最大雨强由62 mm/24 h提高到74 mm/24 h.因此,根据降雨强度和链路距离,通过变色龙算法自适应地调整系统发送端信号脉冲所含的平均光子数,可以提高量子通信系统在降雨背景下的有效性和可靠性.

Optimal mean photon number of decoy state protocol based on chameleon self-adaptive strategy under the background of rainfall

As one of the most common weathers in daily life, the rain can change the atmospheric compositions and humidity in a short time, which may cause non-ignorable attenuation in free-space quantum communication system. Besides, the absorption and scattering effects caused by raindrops can also bring huge attenuation to photon's propagation. In order to solve this burst interference caused by rain weather, optimal mean photon number per pulse and chameleon self-adaptive algorithm (CSA) are proposed based on the rainfall distribution model and decoy-state quantum key distribution. Due to the lack of producing mature ideal single photon source technology, the decoy-state protocol with highly attenuated laser becomes the most practical and most widely used quantum secure communication protocol currently. Among all the different kinds of decoy-state protocols, the vacuum+weak decoy state quantum communication secure protocol is chosen to be the basis of our research. Besides, in order to study the influence of mean photon number per signal pulse, we set the pulse ratio between signal state, decoy state and vacuum state to be fixed at 2:2:1. Since the performance of the vacuum+weak decoy state quantum communication system is closely related to the mean photon number per pulse, it is very necessary to confirm the optimal value. Combining the Weibull rainfall distribution model and Mie scattering theory, we first analyze the attenuation caused by rainfall in a free-space quantum communication system. Then the functional relationship among μ_opt, rainfall intensity (J) and link distance (L) is built by studying the propagation of highly attenuated laser in depolarizing channel. Finally, two parameters, secure key rate and channel survival function, are chosen to evaluate the system's performance of reliability and validity. These two parameters are respectively compared between the system with and without CSA. Simulation results show that, as J=30 mm/24 h, L=30 km, the secure key generation rate rises from 2×10^-4 up to 3.5×10^-4 when using the CSA in the quantum communication system; as J=60 mm/24 h, L=20 km, the quantum channel survival function value increases from 0.52 to 0.63; as the quantum channel survival function value is required no lower than 0.5, the rainfall intensity in which quantum communication system can survive rises from 62 mm/24 h up to 74 mm/24 h. These results prove that there is a close relationship between μ_opt and the channel parameters of the quantum communication system under the background of rainfall. Therefore, it is necessary for us to self-adapt the μ_opt value by combining rainfall intensity with the CSA strategy if the reliability and survivability of free space quantum communication system are required to be improved.