Chen Chunyi, Yang Huamin
Opt Express. 2018 Jun 25;26(13):16422-16441. doi: 10.1364/OE.26.016422.
Common randomness arising from turbulence-induced signal fading in reciprocal optical wireless channels is a beneficial resource that can be used to generate secret keys shared by two legitimate parties. The concept of optical wireless channels using common-transverse-spatial-mode coupling (CTSMC) that can maintain perfect fading reciprocity in atmospheric turbulence is first developed in a general manner. Subsequently, by performing Monte Carlo simulations, the Johnson SB probability distribution is demonstrated to be appropriate for statistical description of turbulence-induced signal fading in an optical wireless channel constructed by use of two identical CTSMC transceivers, and the nature of correlation between signal fadings detected by two contiguous reception spatial modes is further quantitatively characterized, revealing that rapid spatial decorrelation between signal fadings observed by a legitimate party and an eavesdropper holds for scenarios of practical interest. Finally, the information theoretic capacity for generating secret keys from CTSMC-based optical wireless channels is theoretically formulated and quantitatively examined under different conditions, manifesting that the turbulence strength and average electrical signal-to-noise ratio have a noticeable combined impact on the secret key capacity, especially in the far-field case.
在互易光无线信道中，由湍流引起的信号衰落产生的公共随机性是一种有益资源，可用于生成两个合法方共享的密钥。首先以一般方式提出了利用共横向空间模式耦合（CTSMC）的光无线信道概念，该概念可在大气湍流中保持完美的衰落互易性。随后，通过进行蒙特卡罗模拟，证明约翰逊SB概率分布适用于对使用两个相同CTSMC收发器构建的光无线信道中湍流引起的信号衰落进行统计描述，并进一步定量表征了由两个相邻接收空间模式检测到的信号衰落之间的相关性，揭示了在实际感兴趣的场景中，合法方和窃听者观察到的信号衰落之间存在快速的空间去相关。最后，从理论上推导并在不同条件下定量研究了基于CTSMC的光无线信道生成密钥的信息理论容量，表明湍流强度和平均电信噪比对密钥容量有显著的综合影响，尤其是在远场情况下。
