In this paper, the physical layer security (PLS) analysis for a decode-and-forward (DF) protocol based multi-hop hybrid radio frequency (RF)/ free space optics (FSO) is presented. Herein, two different scenarios are considered for detecting the secured information at the destination. In the first scenario, at each hop, the received signals with higher secrecy capacity are selected. However, in the second scenario, the RF and FSO signals are simply decoded and forwarded to the next hop and selection is done at the last hop only. Each node in the system is connected to its subsequent node through parallel RF and FSO links. The FSO links and RF links are characterized by Málaga (
M) and Nakagami-
mcomposite distributions respectively. For both scenarios, the secrecy outage probability (SOP), strictly positive secrecy capacity (SPSC), intercept probability (IP), and effective secrecy throughput (EST) are obtained as performance metrics. These performance metrics are obtained by considering pointing error, different optical signal detection methods, turbulence effect, and the RF link fading parameter (
m). Using the results, the security and reliability trade-off analysis is discussed for two scenarios. In addition, the asymptotic results are also obtained to study the system in depth. Further, the secrecy diversity order (SDO) and secrecy coding gain (SCG) are obtained to analyse the system in depth. Finally, Monte-Carlo Simulation is performed to verify the obtained results. The results manifest that the scenario with selection at each hop provides better secrecy performance than the scenario with selection at the last hop.
This paper analyzes the physical layer secrecy (PLS) performance of a hybrid free space optical and radio frequency (FSO/RF) communication system under a modified selection combining scheme. The transmission scheme takes into account secrecy performance as well as diversity gain and ease of implementation. The effects of FSO link, namely the FSO atmospheric turbulence and the FSO receiver pointing error, are included in the analysis while the power amplifier (PA) inefficiency for the RF transmission is considered to have more realistic understandings on the system performance. The exact analytical expressions for the performance indicators including the average secrecy capacity (ASC) and secrecy outage probability (SOP) of the investigated mixed FSO/RF system are derived. The asymptotic SOP analysis reveals useful insights into the performance of the investigated mixed system. Analytical and simulation results are presented to evaluate the PLS performance of the proposed mixed system as well as to compare the performance of other hybrid systems with different setups.