Multi-hop coherent free-space optical communications over atmospheric turbulence channels

Abstract

In this paper, we investigate multi-hop relaying as an efficient fading mitigation tool for coherent free-space optical (FSO) systems over atmospheric turbulence channels. We consider an FSO relaying system with decode-and-forward relay nodes and multiple heterodyne receivers with modal compensation. Based on a recently introduced statistical characterization for the combined effects of log-normal turbulence fading and modal compensation, we derive the outage probability and quantify the potential performance improvements through the derivation of diversity multiplexing tradeoff (DMT) and diversity gain. Our outage analysis yields impressive power savings for multi-hop relaying even with a single-relay. In addition, the DMT analysis in practical signal-to-noise ratio (SNR) ranges demonstrates that multi-hop transmission scheme improves finite-SNR diversity gain throughout the range of the multiplexing gain.