BER analysis of all-optical AF dual-hop FSO systems over Gamma-Gamma channels

In this paper, we analyze the performance of all-optical dual-hop free-space optical communication (FSO) systems over strong atmospheric turbulence channels. In our analysis, turbulence channels are modeled by Gamma-Gamma distribution and dual-hop transmission is based on optical amplify-and-forward (OAF) technique. We formulate both exact-form and closed-form expressions for bit-error rate (BER) of M -ary pulse-position modulation (PPM) dual-hop FSO systems taking into account the effects of various noises as well as path loss and geometric spreading of optical beam. The numerical results show that strong turbulence has a severe effect on the performance of FSO systems. In addition, background noise and thermal noise at the destination are dominant compared to other terms of noise from the source and the relay. Thanks to OAF technique, the required transmitted power is reduced accordingly to the amplifier gain thus the transmission distance can be extended.