Performance analysis of PPM modulation in multihop FSO system over gamma gamma channel

Atmospheric turbulence induced fading is one of the main impairments affecting the operation of free-space optical (FSO) communication systems. In this work, the average symbol error rate (SER) of M-ary pulse position modulation (PPM) is analyzed under Gamma-Gamma fading channel. Using the characteristics of Meijer G function, Closed-form expression for average SER is derived. In this paper, we analyze the performance of detect and forward relay or/and amplify and forward three-hop FSO systems over strong atmospheric turbulence channels. In our analysis, turbulence channels are modeled by Gamma-Gamma distribution and the AF transmission is based on optical amplify-and forward (OAF) technique. The DF relay refers to detect and forward protocol. We look for symbol-error probability (SEP) of dual-hop PPM modulated 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. we employ PPM modulation to improve the system's performance.