Multiple user pair scheduling in TWR assisted FSO systems

In this paper, various multiuser scheduling schemes are applied to a two-way relay (TWR) assisted multiple user pair free-space optical (FSO) communication network, when the optical beam is subjected to path loss, misalignment errors, and atmospheric turbulence. The FSO network consists of a single, half-duplex, decode-and-forward, two-way optical relay that serves multiple user pairs by employing a scheduler. Three types of schedulers based on absolute signal-to-noise ratio (SNR), normalized SNR, and selective multiuser diversity are considered. Further, the atmospheric turbulence is modeled by a recently proposed statistical model, namely the Málaga M-distribution. For the presented system and channel models, closed-form and asymptotic expressions for outage probability and bit error rate are derived. The mathematical analysis is accompanied by Monte Carlo simulations and several numerical examples to illustrate the effect of the key system parameters.