Performance of APD-based amplify-and-forward multihop FSO systems over turbulence channels

We propose and theoretically analyze the performance of amplify-and-forward (AF) multihop free-space optical (FSO) systems using avalanche photodiodes (APD) over lognormal turbulence channels. Both serial and parallel relaying configurations are considered, and each AF relay node is constructed by using an APD for signal amplification. At the destination node, APD receiver is used, and in order to simplify the signal detection, the subcarrier binary phase-shift keying (SC-BPSK) signaling is assumed. In the performance analysis, we use the Fenton-Wilkinson approximation method to analytically derive the closed-form expression of the outage probability taking into account the atmospheric turbulence, amplifying noise cased from APD as well as APD receiver noise at the destination node. MonteCarlo simulation is also performed and a good agreement between the analytical and simulation results is confirmed.