Performance Evaluation of Dual Hop Mixed FSO RF System Using Differential Chaos Shift Keying With Secrecy Analysis

Free space optical (FSO) communication system is a promising candidate for today's era of intelligent networks for the reason that it has potential advantages such as, high data rates, large bandwidth, non-licensed spectrum, line-of-sight communication and many more. Relay-assisted communication provides an additional boost to system's performance by expanding its capacity, coverage range, enhancing data rates and mitigating the effect of turbulence. In this manuscript, three dual-hop systems are considered i.e., FSO-FSO, radio frequency (RF)-FSO and FSO-RF systems employing decode and forward (DF) relaying protocol. Furthermore, chaotic signals are incorporated in these systems to enhance their confidentiality using differential chaos shift keying (DCSK). This is demonstrated by performing secrecy analysis on the system. Here, it is assumed that RF link experiences Nakagami-m fading while the affect of fading in FSO channel is caused by Gamma-Gamma turbulence along with pointing errors. The average bit error rate (BER) of three proposed systems is analyzed, and the results indicated that the FSO-RF-DCSK system outperformed the other three in terms of performance. Finally, secrecy performance is accomplished using secrecy outage probability (SOP) as a metric for the proposed systems. The findings are noteworthy as FSO-FSO-DCSK system demonstrates superior performance as compared to FSO-RF-DCSK and RF-FSO-DCSK systems in terms of secrecy. As compared to other counterparts, FSO-FSO-DCSK system shows an improvement of more than 10 order of magnitude in terms of signal-to-noise (SNR) ratio.