On the physical layer security of hybrid RF-FSO system in presence of multiple eavesdroppers and receiver diversity

Abstract

This paper investigates the physical layer security (PLS) performance analysis for dual hop mixed radio frequency (RF)-hybrid RF/free space optics (FSO), the first hop is considered as RF and second hop consists of two independent RF and FSO links and hybrid RF-RF/RF-FSO with two separate dual hop paths including RF-RF and RF-FSO links. The communication takes place in the presence of RF as well as optical based eavesdroppers which are trying to intercept the signal from legitimate links. Moreover, considering an urban environment the RF links are modelled by Rayleigh distribution and the FSO links are characterized by Málaga (M) distribution. To investigate the system, secrecy performance metrics such as secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived in its closed form. The effect of selection combining (SC) and maximal ratio combining (MRC) diversity techniques on the system performance is also depicted. In addition, some practical issues of FSO links such as the effect of atmospheric turbulence, optical signal detection techniques and pointing error effects on the system performance are discussed. To get more insight, the asymptotic expressions are obtained for each scenario. Then the results are compared with results obtained for mixed FSO/RF system and also discussed in brief. Finally, the results are verified through Monte-Carlo simulation.