A novel secrecy-based switching mechanism for hybrid FSO/RF systems

The integration of Free Space Optics (FSO) and Radio Frequency (RF) communication systems has recently gained attention from researchers worldwide as a promising solution to enhance beyond 5G wireless networks. A hybrid FSO/RF system can exploit the benefits of both technologies to improve throughput, security and/or reliability. The most common style of hybrid FSO/RF systems is to activate only one of them at a time using a pre-defined switching mechanism that is usually designed to maintain link's reliability or improve throughput. In this paper, a novel switching mechanism that aims to enhance the security level. Specifically, the secrecy capacity of each link will be first computed and the link whose secrecy capacity is better will be activated. Different types of eavesdroppers and various weather conditions are considered. Analysis is conducted following a solid mathematical framework to derive the average channel capacity, the average secrecy capacity and the link utilization percentage of each of the links, aiming to formulate the average secrecy capacity of the proposed hybrid FSO/RF switching mechanism. Interesting results reveal that when the RF link is being eavesdropped, the non-eavesdropped FSO link is activated unless the weather is rainy and the transmission distance is short. Also, when FSO link is being eavesdropped, the non-eavesdropped RF link is always preferred. On the other hand, when both links are subject to eavesdropping and weather is either hazy or rainy, both links are being almost equally utilized at short transmission distances, while RF is always utilized at long transmission distances.