Novel Adaptive Transmission Algorithms for Free-Space Optical Links

Atmospheric turbulence is a major degrading factor in free-space optical (FSO) systems. Since turbulence-induced fading results in a very slowly-varying channel, reliable feedback is possible allowing the implementation of adaptive transmission in practical FSO systems. In this paper, we propose adaptive transmission algorithms in which transmit power and/or modulation size are varied according to the channel conditions. The design of adaptive algorithms is formulated as optimization problems of spectral efficiency and average power consumption at a targeted value of outage probability under peak power constraints. The proposed adaptive schemes bring significant improvements over their non-adaptive counterparts.