Optimised Gain Saturated Pre-Amplified Free-Space Optical Communication Systems

The performance of a fixed and saturated gain preamplified free-space optical communication system in a turbulent atmosphere is investigated, in the presence of amplified spontaneous emission noise. Bit error rate (BER) analysis of both non-adaptive decision and adaptive decision threshold schemes are considered and the effects of using both fixed and saturated gain preamplified receivers are investigated for different turbulence regimes. Results obtained in this paper showed, as expected, that the lognormal distribution gives a better performance than the gamma-gamma distribution in the weak turbulence regime and that the BER performances reaches an optimal level when the power at the preamplifier input is comparable with the internal saturation power of the preamplifier. Also, it is shown that the optimal non-adaptive decision threshold in a gain saturated preamplified receiver will have a decision threshold level between 0.2 and 0.3.