Performance analysis of relay-assisted NLOS ultraviolet communications over turbulence channels

Ultraviolet (UV) communication enables non-line-of-sight (NLOS) outdoor wireless connectivity and is particularly desirable for relaxing or eliminating pointing and tracking requirements of infrared links. In the current literature, atmospheric turbulence effects are typically ignored under the assumption of short link distances. In this paper, we consider a multi-hop UV system with decode-and-forward relaying and analyze its performance in the presence of log-normal (LN) turbulence. Specifically, we assume that each NLOS link consists of two line-of-sight (LOS) paths, each of which experience LN distributed fading.We first obtain a closed-form expression for the statistical distribution of turbulence-induced fading in NLOS UV links. Then we obtain the outage probability of the multi-hop UV system and quantify diversity gain as a function of system and channel parameters. Our results show that, with proper choice of these parameters, the turbulence variance for the NLOS link can be lower than that of the LOS link. This in turn yields higher-diversity gains. We also present numerical results to confirm the accuracy of our derivations and discuss the effect of several system parameters on the outage probability and diversity gain.