Opportunistic cooperation for FSO links aided by decode and forward relay

User cooperation technique has been employed lately as a means to provide diversity against turbulence induced fading. In this paper, we consider opportunistic user cooperation to further enhance the performance and robustness especially when the link from the source to the relay has a deteriorated quality. The discussion concerns a three-way scenario in which intensity modulation and direct detection are adopted in the transceivers of the source, a decode and forward (DF) relay and the destination. The figure of merit to evaluate is the outage probability and the analysis assumes the presence of Gaussian noise. To substantiate the improvement in performance, we adopt direct transmission and deterministic user cooperation as the benchmarks for comparison through both analytical study and Monte-Carlo simulation.