On the Capacity of Decode-and-Forward FSO System With Single- and Dual-Hop RF Link

Abstract

In this study, we consider two dual-hop FSO systems with decode-and-forward protocol. The FSO system is assumed to be equipped with RF link used as a backup in case the FSO link experiences strong atmospheric turbulence or pointing errors. The two system models differ by the setup of the RF link. A single-hop RF backup link is used for the first system model, whereas a dual-hop RF backup link is used for the second system model. We assume that the FSO system uses intensity modulation with direct detection and the channel is modeled by gamma-gamma distribution, and the RF channel is modeled by Nakagami-m distribution. The performance of both system models is studied in terms of ergodic capacity where new expressions are derived and compared with the results of Monte Carlo simulations. The results indicate the improvement of the spectral efficiency compared to the conventional dual-hop FSO system.

Keywords

• Free space optics
• hybrid system
• strong atmospheric turbulence
• average capacity