Rate-adaptive selective relaying using time diversity for relay-assisted FSO communications

In this paper, a novel cooperative protocol for free-space optical (FSO) communication systems is proposed, wherein the performance analysis is evaluated over gamma-gamma (GG) fading channels with pointing errors. This novel relaying scheme is based on the optical path selection, source-destination (S-D) or source-relay-destination (S-R-D), with a greater value of fading gain or irradiance together with the use of repetition coding (RC), exploiting the potential time-diversity order available in the turbulent channel in order to maintain a high diversity order. A novel closed-form asymptotic bit-error rate (BER) expression is derived for a 3-way cooperative FSO system. A greater diversity gain with one only relay is corroborated by the obtained results if compared with cooperative FSO schemes of similar complexity at the expense of an information rate-reduction (RR).