Performance of Optically Pre-amplified FSO System under ASE Noise with Pointing Errors

Optical pre-amplifier forms an important component of a free space optical (FSO) communication system for improving the receiver sensitivity. The use of an optical preamplifier results into amplified spontaneous emissions (ASE) which dominates the receiver thermal and shot noises. The square law photodetector at the receiver 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 literature. In this paper, we evaluate the bit error rate performance of a FSO system assuming non-return-to-zero onoff keying modulation in the presence of ASE noise under the combined effect of very strong turbulence (modeled by negative exponential distribution) and pointing errors. A further insight into the system is provided by performing the diversity analysis.