Performance Analysis of Hybrid FSO/RF System with Transmit Aperture Selection

This paper presents a multiple-input-single-output (MISO) hybrid free-space optics/radio frequency (FSO/RF) system with transmit aperture selection (TAS) scheme. The proposed system consists of a MISO FSO sub-system with N transmit apertures and a single millimeter wave (MMW) RF link. The MISO FSO sub-system is given higher priority to transmit using the selected best link. The aperture with highest gain at the receiver is considered as the best link. The MMW RF link is used when the FSO sub-system is in outage. The FSO links experience Gamma-Gamma atmospheric turbulence induced fading together with pointing errors. To model the pointing errors, the effect of transmit beam waist, detector size, and jitter variance are considered explicitly for FSO link. The MMW RF link experiences κ-μ shadowed fading. The novel expressions of probability density function (PDF) and cumulative distribution function (CDF) of the MISO FSO sub-system using TAS scheme are derived for generalized N transmit apertures. These expressions are further utilized to derive the exact expressions for outage probability and average SER for the proposed system. The results show that proposed hybrid system outperforms the individual MISO FSO system especially for high pointing errors scenario. The performance improvement is observed with each added link for the proposed system. However, the performance improvement with N
_th
aperture is with less SNR gain compared to (N-1)
_th
aperture.