DF cooperation over Gamma-Gamma fading FSO links with an erroneous relay

In this paper, we analyze a free space optical (FSO) cooperative communication system utilizing the Gamma-Gamma fading optical links and a single decode-and-forward (DF) erroneous relay. We adopt the subcarrier intensity modulation (SIM) technique for transmitting the M-ary phase shift keying (M-PSK) modulated optical data over an FSO link. For the considered DF-FSO cooperative system, we derive an optimum maximum-likelihood (ML) decoder and a sub-optimal piecewise linear (PL) decoder in the destination of the system. The proposed PL decoder performs very close to the ML decoder and provides significantly reduced decoding complexity as compared to the optimal decoder. Both the ML and PL decoders incorporate the possibility of erroneous transmission by the DF relay and require the average statistics of the source-relay link for decoding the data of the source in the destination. We also derive the approximate average symbol error rate (SER) of the proposed PL decoder for M-PSK constellation.