Adaptive Optimization of a Free Space Laser Communication System Under Dynamic Link Attenuation

Free space laser communication is a potentially attractive technology that can offer intrinsically high data rates and resistance to jamming, and facilitates low probability of interception and low probability of detection (LPI/LPD). However, practical links established in the atmosphere are adversely affected by signal attenuation and dynamic turbulence, which can create spatial and temporal variations in the refractive index. The resulting distortions lead to reduced signal power and increased bit error rate (BER), even over short ranges. To overcome possible signal degradation under adverse conditions, laser communication systems must increase power and reduce the communication bit rate. Under dynamic link attenuation both of these parameters can be tuned to optimize performance. In this paper, we present and compare three methods for optimizing optical link efficiency. The work is based on experiments conducted with a commercially available system, and its scaled-down laboratory prototype. The proposed methods demonstrate different degrees of optimization capabilities under practical operating conditions, but, in general, they maintain the highest possible bit rate at the minimum power consumption, while obtaining an acceptable BER.