BER of an optically pre-amplified FSO system under málaga turbulence, pointing errors, and ASE Noise

Abstract

The performance of a free space optical (FSO) communication system is significantly affected by atmospheric turbulence and pointing errors (PEs) apart from the additive noise which is assumed to be Gaussian. The Málaga or M-distribution encompasses various proposed statistical models for atmospheric turbulence in FSO systems. An optical pre-amplifier is an essential component of FSO systems for improving the receiver (Rx) sensitivity. However, optical pre-amplification results in amplified spontaneous emissions (ASE), which dominate the Rx thermal and shot noises. The square law photodetection process at the Rx in a FSO system necessitates the consideration of Chi-square statistics for the decision variable contrary to the Gaussian approximation that is widely used in the literature. In this paper, we evaluate the bit error rate (BER) performance of a FSO system assuming nonreturn-to-zero on-off keying modulation in the presence of ASE noise under M-turbulence and PEs. We also derive asymptotic BER expressions for the considered FSO system for large values of signal-to-noise ratio in terms of simple elementary functions. A further insight into the system is provided by performing the diversity analysis. © 2017 IEEE.