Fade Mitigation Based on Semiconductor Optical Amplifiers

We present and analyze a novel fade mitigation technique that is applicable on outdoor optical wireless systems. Our key idea is to utilize the nonlinear power-dependent gain properties of a semiconductor optical amplifier (SOA) to provide unbalanced amplification between faded and non-faded instances of the optical wireless signal. We analytically demonstrate that this power equalization process smoothes out fade-induced power fluctuations and drastically reduces the probability of the system being in a fade state. In medium to strong turbulence governed by gamma-gamma statistics, our results predict that the fade probability can be reduced by over 80% when the SOA is introduced at the optical wireless receiver. We also show that the duration of remaining fades is reduced by a sizeable percentage, and a percentile reduction of the average fade duration of over 85% can be achieved at the SOA output.