Performance analysis of adaptive combining based hybrid FSO/RF terrestrial communication

Abstract

This study deals with the performance analysis of adaptive combining-based hybrid free-space optics (FSO)/radio-frequency (RF) system in a terrestrial communication scenario with and without pointing errors. Here, outage probability and average symbol error rate (SER) are used as the performance metrics. Adaptive combining is a switching scheme in which the FSO link is active throughout, whereas the RF link is activated based on the transmission reliability of the FSO link and maximal-ratio-combining (MRC) of RF and FSO links is performed at the destination. The small-scale fading in RF and atmospheric turbulence induced fading in FSO links have been characterised by Nakagami-m and Gamma–Gamma distributions, respectively. In addition, the radial displacement between the beam centre and detector centre, which induces pointing errors, is modelled using Rayleigh distribution. The exact closed form expressions for the outage and average SER have been derived along with their corresponding asymptotic expressions. Diversity gain of the system has also been determined using the asymptotic expressions. Further, the variation in the performance of the system has been analysed with respect to various parameters including link distance, fading severity parameter, average signal-to-noise of the RF link, and the pointing errors parameter.