电离层偶发E层是指在距离地面高度80-150 km之间,在风剪切作用下,电子密度急剧增加的不规则电离薄层,它会对量子卫星光信号的传输造成极大的影响.然而,有关电离层偶发E层与星地间量子通信信道参数关系的研究,迄今尚未展开.为了研究偶发E层对量子卫星通信性能的影响,首先分析了它的形成过程,得出自由电子密度随高度变化的关系;然后建立了自由电子密度、偶发E层的厚度对量子卫星链路衰减的模型;针对振幅阻尼信道,给出自由电子密度对信道容量、纠缠保真度、误码率和安全密钥产生率的定量关系.理论分析和仿真结果表明,当偶发E层的厚度为1 km、电子密度由3×105 cm-i增加到27×105 cm-1时,信道容量由0.8304衰减到0.1319,纠缠保真度由0.9386下降到0.3606,量子误码率由0.0093增加到0.0769,安全密钥产生率由9.968×10-5减小到1.91×10-6.由此可见,电子密度的大小和偶发E层的厚度对量子卫星通信性能有显著的影响.因此,在进行量子卫星通信时,应根据对电离层参数的探测情况,自适应调整卫星系统的各项指标,以确保量子通信的可靠性.%Quantum communication is a brand new way of communicating,in which the quantum entanglement effect is used to transmit information.Quantum communication is a new interdisciplinary subject between quantum theory and information theory.It has advantages of perfect information security and higher efficiency in transmission.The successful launch of the first quantum satellite named Micius laid an important foundation forconstructing a secure quantum communication network on a global scale.On the other hand,in the process of quantum satellite communication,the atmospheric environment near the ground will have a certain influence on the transmission of quantum signals,so the security of quantum communication is reduced.One of the influence factors is the ionospheric sporadic E layer.In the actual quantum communication environment,when the weak coherent state light source is simulated the single photon,the source energy is attenuated if the quantum signal passes through the ionosphere.On a space scale of 80-150 km off the ground,the ionospheric sporadic E layer is an irregular thin layer,in which there occurs a sharp increase of electron density under the action of wind shear.Sporadic E layer has a great influence on quantum satellite signal transmission.However,the research about the relationship between the sporadic E layer and quantum communication channel parameters has not yet conducted.To investigate the influence of the ionospheric sporadic E layer on the performance of quantum satellite communication,sporadic E layer formation process is first analyzed.And then the relationship between the free electron density and the height is obtained.After that,the model of the free electron density,the formation thickness and the link attenuation of quantum satellite is established.According to the amplitude damping channel,the quantitative relationships among free electron density and the channel capacity,entanglement fidelity,the quantum bit error rate and the secure key rate are put forward and simulated finally.Theoretical analysis and simulation results show that when the thickness is 1 km,the electron density increases from 3 × 105 cm-1 to 27 × 105 cm-1,the channel capacity decreases from 0.8304 to 0.1319,the entanglement fidelity decreases from 0.9386 to 0.3606,the quantum bit error rate increases from 0.0093 to 0.0769,and the secure key production rate decreases from 9.968 × 10-5 to 1.91 × 10-6.It can be shown that the electron density and the thickness of sporadic E layer have significant effect on the performance of quantum satellite communication.Therefore,in the process of quantum satellite communication,in order to ensure the reliability of quantum communication,based on the detection of ionosphere parameters,the various indexes of the satellite system should be adjusted adaptively.
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