为了研究由太阳活动引起的X射线耀斑对星地量子链路通信性能的影响，本文基于Chapman理论构建了电离层电子密度增量模型，并基于此模型得到了关于X射线辐射通量及太阳天顶角的电离层额外衰减因子。通过仿真分析了基于均值的加权信道容量、基于区间的加权信道生存函数、量子信道建立速率及量子密钥分发系统误码率随X射线耀斑辐射等级的变化情况。结果表明，在X射线耀斑干扰下，电离层电子密度最大增量可达2.78?10^6 cm^-3；当光量子信号穿过厚度为1 km的电离层，X射线耀斑辐射通量由10^-5 W/m^2增至10^-4 W/m^2时，均值加权信道容量衰减幅度为0.142 bit/s；当X射线耀斑辐射强度由10^-5.5 W/m^2增至10^-4.25 W/m^2，区间加权信道生存函数由0.986衰减至0.799，信道维持高效服务状态的能力大幅降低；当加权信道保真度F=0.92时，随着X射线辐射通量由10^-5.2 W/m^2增至10^-4.4 W/m^2,当信号传输距离为6 km时信道建立速率由18对每秒衰减至7对每秒；当传输距离为15 km, X射线耀斑辐射等级为heavy时，密钥分发系统误码率高达0.021，且该误码率会随着电子密度的增加而增加。因此，X射线耀斑对星地量子通信链路的影响不容忽视，可根据X射线耀斑辐射等级适当调整量子卫星的各项参数指标以保证通信的可靠性与有效性。

In order to study the impact of X-ray flares caused by solar activities on the communication performance of the quantum satellite-terrestrial link, this paper constructs an ionospheric electron density increment model based on Chapman theory, and obtains the ionospheric extra attenuation factor about the X-ray radiation flux and the solar zenith angle based on this model. The variations of mean-based weighted channel capacity, interval-based weighted channel survival function, quantum channel establishment rate and quantum key distribution system BER with X-ray flare radiation level are analyzed by simulation. The results show that under the interference of X-ray flares, the maximum increment of electron density in the ionosphere can be as high as 2.78?10^6 cm^-3；The interval-weighted channel capacity attenuation is 0.142 bit/s when the photonic quantum signal passes through the ionosphere with a thickness of 10 km and the X-ray flare radiative flux increases from 10^-5 W/m^2 to 10^-4 W/m^2; When the X-ray flare radiation intensity increases from 10^-5.5 W/m^2 to 10^-4.25 W/m^2, the weighted channel survivor function decays from 0.986 to 0.799, and the ability of the channel to maintain an efficient service state decreases significantly; When weighting the channel fidelity F=0.92, the channel establishment rate decays from 18 pairs per second to 7 pairs per second as the X-ray radiation flux increases from 10^-5.2 W/m^2 to 10^-4.4 W/m^2 , when the signal transmission distance is 6 km; When the transmission distance is 25 km and the X-ray flare radiation level is heavy, the BER of the key distribution system is as high as 0.021, and the BER increases with the increase of electron density. Therefore, the impact of X-ray flares on the satellite-terrestrial quantum communication link should not be ignored, and the parameter indexes of the quantum satellite can be adjusted appropriately according to the radiation level of X-ray flares to ensure the reliability and effectiveness of the communication.

TN929.12

国家自然科学基金项目（61971348，61201194）