An enhanced security algorithm for wireless communication system deploying hybrid free space optical (FSO)-millimeter wave (mmWave) links is proposed in this clause. The activation of either links, FSO or mmWave, is determined through index modulation (IM) technique. In particular, the first bit to be transmitted determines the active link; while remaining bits modulate a conventional symbol to be transmitted over the active link. Yet, before transmitting the symbol, it is precoded by another signal that is extracted from the channel coefficient of the active link. The channel coefficients for both links are assumed to be available at the transmitter and the receiver through typical channel estimation algorithms. It is revealed that the security of the proposed system is significantly enhanced, where IM concept degrades the performance of an eavesdropper who is attacking any of the communication links. Also, the use of precoding worsens the functioning of an eavesdropper who is attacking both links. The impact of channel estimation errors along with the spectral efficiency, turbulence conditions, channel fading, and eavesdropper capability on the overall performance is investigated and thoroughly discussed.

中文翻译：

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基于安全索引调制的混合自由空间光和毫米波链路


本节提出了一种用于部署混合自由空间光（FSO）-毫米波（mmWave）链路的无线通信系统的增强安全算法。 FSO 或毫米波链路的激活是通过索引调制 (IM) 技术确定的。特别地，要发送的第一个比特确定活动链路；而其余比特则调制要在活动链路上传输的传统符号。然而，在发送符号之前，它由从活动链路的信道系数中提取的另一个信号进行预编码。假设两条链路的信道系数可通过典型的信道估计算法在发射机和接收机处获得。据透露，所提出的系统的安全性显着增强，其中 IM 概念降低了攻击任何通信链路的窃听者的性能。此外，预编码的使用会恶化攻击两个链路的窃听者的功能。研究并深入讨论了信道估计误差以及频谱效率、湍流条件、信道衰落和窃听能力对整体性能的影响。