Abstract
In Radio Frequency (RF)-Free Space Optical (FSO) mixed links, secrecy capacity (SC) can be improved by exploiting spatial diversity (i.e., antenna diversity) in the RF path. In addition to atmospheric turbulence and point error of the FSO link, antenna correlation in the RF link can significantly deteriorate the secrecy performance. In this paper, a secrecy rate of wiretap channels with a single source, relay, destination, and eavesdropper is analyzed under practical environments with the aforementioned impairments. The RF hop (source-to-relay) and the FSO hop (relay-to-destination) are modeled utilizing arbitrarily correlated Nakagami- $m$ and Malaga ( $\mathcal {M}$ ) distributions, respectively. The correlated signal branches of the RF hop are combined at the relay exploiting equal gain combining reception technique. We assume that the eavesdropper is capable of wiretapping via RF and FSO links separately. We derive novel closed-form expressions for secrecy outage probability (SOP) and strictly positive secrecy capacity (SPSC) considering heterodyne detection (HD) and intensity modulation with direct detection (IM/DD) techniques in order to examine the impact of atmospheric scintillation, pointing error, fading, and correlation on the system's secrecy performance. It is shown that the HD technique exhibits a better performance than an IM/DD technique. In addition, similar to the pointing error and turbulent fading, the correlation imposes a detrimental impact on SC. Finally, Monte-Carlo simulation results are provided for validation of the derived expressions.
Highlights
1.1 Background StudyIn the last few years, data traffic in the radio frequency (RF) range has increased at an unprecedented rate
Substituting (11) and (14) into (22), the lower bound of secrecy outage probability (SOP) can be denoted as vR −1 (2cR φ )i i!
This is expected since the lower cost and reduced complexity of intensity modulation with direct detection (IM/DD) technique permits a limited number of modulation schemes, and this, in turn, restricts its performance
Summary
In the last few years, data traffic in the radio frequency (RF) range has increased at an unprecedented rate. FSO has comparatively higher speed and larger bandwidth. A mixed RF-FSO system has been suggested as a possible solution to overcome the limitations of both technologies. In this network, complete communication is divided into two phases. The larger portion of the network, i.e. the path between the source and relay (R), is covered utilizing RF technology. The relatively smaller distance, i.e. the relay to destination link, is covered utilizing FSO technology. The shorter range and comparatively higher speed, i.e., wider bandwidth, warrant FSO as an interesting prospect for solving the problem with the last mile access [11]
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