Comparative Analysis of BER Performance for Direct Detection and Coherent Detection FSO Communication Systems

Free space optical (FSO) propagation over atmospheric turbulence affected by fluctuations in both intensity as well as in phase of received signal. This result decreases electrical signal to noise ratio (SNR) and because of this degradation it impaired performance. In this paper, we are discuss a comparative analysis of bit error rate (BER) performance for the on-off keying (OOK) modulated direct detection and coherent detection FSO communication systems in weak turbulence conditions. We present a statistical channel model called as log-normal distribution to describe the irradiance fluctuations in weak turbulence for FSO communication systems. First, we investigate performance of the direct detection FSO system over the log-normal turbulence channel and derived the closed form expression for BER in term of average received irradiance and SNR, and then we do same for coherent detection FSO system, finally, compare both of them.