Performance Study of Serial Relay OFDM FSO System under QPSK Modulation

In this paper, we study the performance of serial relay coherent OFDM free space optical (FSO) communication system by quadrature phase shift keying(QPSK) modulation under strong atmospheric turbulence conditions. The relay assisted FSO system adopts decode and forward (DF) relaying protocol between source and destination of relay assisted link. Considering the joint effect of the light intensity flicker of the atmospheric turbulence, the loss of the path and the transmitter and receiver's pointing error on the atmospheric channel fading model, the closed form expressions of the outage probability and the symbol error rate (SER) of the system under the negative exponential distribution and the K distribution model is derived respectively. The effects of key factors such as the number of system hops, the number of subcarriers and average signal-to-noise ratio (SNR) on the outage and SER performance of the multihop OFDM FSO system are analyzed by simulation.