Diversity orders and coding gains of repetition coding and transmit laser selection over MIMO free-space optical links

In this paper, we analyze the repetition coding and transmit laser selection schemes over multiple-input-multiple-output free-space optical communication systems with intensity modulation and direct detection over gamma-gamma atmospheric turbulence channels. We derive novel closed-form expressions for the outage probabilities achieved by the above schemes. Through an asymptotic analysis of the outage probabilities, we prove that both schemes achieve the same diversity order that is equal to the product of the number of transmit apertures, number of receive apertures and a channel related parameter. We also prove that the superiority of the transmit laser selection scheme over the repetition coding scheme resides in a coding gain that we quantify analytically in this work.N/